Time to get a cleaner crew...

[LadAShark]

I was on reef cleaners earlier, so I just saw some real cool stuff there. You should check that out.

From them I'd order:
20 dwarf cerith
10 Florida ceriths
5 limpets (because they're cool)
5-10 nassarius snails (depending on sand grain size and dirtiness)
10 assorted hermit crabs (for fun)
3-5 scarlet hermits (because they're great and peaceful)
5-10 blue legs
The one penny macro algae
30- zig zag periwinkles
1 coral banded shrimp

Reasons:
Each of these snails covers a different area
Ceriths = top of sand
Nassarius = inside sand
Limpets = glass and rock
Zig Zag Periwinkles = glass and rock (and they're super cheap).

As far as hermits go, Scarlets are vibrant and effective. They just aren't super interesting to watch.

Assorted hermits is a grab bag, but you may get something cool or fun to watch. Or something that eats something that nothing else will eat like hair or bubble algae. However you should watch these to make sure they aren't eating things you like.

What I wouldn't get:
Any mithrax crab.
(They are veracious and without a good food source, they can go rouge. If you have bubble algae or you feed them, they're super cool)

A brittle star
(Requires direct feeding once they get above 6-7 inches in diameter. Once they get that big they have a bigger appetite than detritus can supply and your CUC starts looking really tasty).

Short spine urchin:
Just get a pencil urchin, they're better and less dangerous. And cheaper.

Peppermint shrimp
Will go rouge if you don't have aptasia.

Zebra hermits
These guys are ******s. They have a strict hierarchy, will fight for shells, and they don't even like algae! They only eat left over fish food and other detritus. They will walk all over corals too and bother them. They're villainous little buggers.
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That said, most people's mistake is that they put the CUC in long before the fish and other livestock. They're put in a basically empty tank with little food except for each other. Those that are needed for cleaning up later on will starve and those that don't matter as much survive.

I wouldn't suggest a pencil urchin. Over on shark and ray central, there was a guy whose baby coral catsharks were being hunted down by a pencil urchin. They are carnivores, so beware.

I would just avoid crabs altogether. All of them seem capable of going rogue in the right circumstances. Of course, this is just my opinion, especially because what I'm interested in are predators tanks, so crabs are either small enough to be snacks, or big enough enough to be threats. Most hermits can, however, get a taste for snails, fish, or even corals.

The reason why so many people start with CUC is because they want the inverts to establish themselves before introducing fish that would otherwise hunt them down. I'm pretty sure you can introduce the cuc first, IF you have food for each type of critter you're introducing. With predator tanks, I dare you to try introducing CUC when the fish are feeling comfortable. Otherwise, if the critter is heavily armored or you're keeping a reef tank, it should just be fine to introduce CUC as you go.

 

[Roboson]

Pencil urchins are omnivores, like most urchins, but they're incredibly slow and their spines aren't dangerous like other urchins. They algae, sponges and sessile inverts, but not fish. They're scavengers, so if they're eating something big like a fish or large crab, it's because it's already dead or it's very sick.

That said, if you could get the link to that, I'd love to read about killer pencil urchins.

Yeah, crabs are always a calculated risk. You have to feed them directly if their food is scarce. And with hermits you HAVE to have extra shells of various sizes and opening shapes. Otherwise snails are at risk. Especially for hermits who's carapace is about 1 inch across or more.

Yeah, CUC goes in first. But some people put it in weeks in advance and don't feed them. That's a recipe for disaster.

 

[LadAShark]

Pencil urchins are omnivores, like most urchins, but they're incredibly slow and their spines aren't dangerous like other urchins. They algae, sponges and sessile inverts, but not fish. They're scavengers, so if they're eating something big like a fish or large crab, it's because it's already dead or it's very sick.

That said, if you could get the link to that, I'd love to read about killer pencil urchins.

Yeah, crabs are always a calculated risk. You have to feed them directly if their food is scarce. And with hermits you HAVE to have extra shells of various sizes and opening shapes. Otherwise snails are at risk. Especially for hermits who's carapace is about 1 inch across or more.

Yeah, CUC goes in first. But some people put it in weeks in advance and don't feed them. That's a recipe for disaster.

I thought pencil urchins were purely scavengers too, but http://z8.invisionfree.com/Sharks_and_Rays/index.php?showtopic=2675
Suggests it is not necessarily so. There's a reason they are considered not reef safe. There's a possibility you might not be able to see what's posted unless you log in, so here's the three most important updates:

11:28, Aug 19, 2014: "At 7pm my coral catshark pup was swimming around looking for food. All normal. When I went to feed them at 945 my pencil urchin had enveloped the coral cat and was eating it. There was a small mark the pups head so I am not sure if a bamboo pup i had the same tank bit her first. I had to pull really hard to get the dead pup from the urchin. Did the urchin catch the pup and eat it alive? Im so freaked out. All other pups are eating and loom good. I separated the bamboo pups into another tank and fired my urchin into the sump. Anyone have any ideas? I will test the water when I get home tonight. All visual indicators such as my corals look good, but I will test to be sure. So shocked and disappointed."

8:58 pm Aug 19, 2014: "I got my answer. I placed one of the bamboos back in with the coral cats. About 2 hours after they all ate I saw the 3 remaining coral cats go to the other side of the tank. The bamboo walked over after them. I figured he would tuck up next to them. He pot shotted one. I couldnt believe my eyes. He went after another before I snatched him out. Mystery solved. Last bamboo I will ever own. I already traded them just gotta wait until they are ready to take possession. Good riddance."

Last update, 7:13 PM, Feb 11, 2015 "I have an update on this. I do not believe the bamboo killed the coral cat. I believe the culprit was the pencil urchin. I moved the pencil urchin in with a pair of pink skunk clowns. The urchin caught one of the clowns sleeping. It had enveloped the clown and the clown was struggling to get away. I happened to be in the room when it happened. I had to break a spine on the pencil urchin to free the clownfish. The clown is still alive and well weeks later so no doubt about it. No pencil urchins in with pups. I wrongly accused the bamboo due to the aggression during feeding."

As for the crabs, you're pretty much guaranteed to have some crab on snail predation at some point, no matter how hard you try, if you keep the two together.

 

[DLHDesign]

Thanks @LadAShark and @Roboson - really appreciate the continued discussion.

At the moment, every snail I've put into the tank dies near instantaneously. All of them have been purchased from the LFS. The most recent (2 astraea) I drip-acclimated for a bit before adding them in (I now understand that this shouldn't be needed, but the LFS water - 1.015 and 5.8dKH - was pretty different from my water). They were doing okay in 50 LFS/50 my water until the container fell over and dumped all the water out (sigh), so I had to add them into the tank. They were dead within the hour. I considered that they might just be dormant, so I put them into a separate container of tank water and have been watching them for a few days (even did a partial water change with new tank water at one point). They are still limp and haven't moved, so I'm pretty sure they are dead too. I guess I should test the water they are in and confirm (high ammonia should indicate that, I'd think?)...

My tank is still recovering from the first die-off of all the snails I added, so my plan is to wait until my ammonia is back to 0 for a few days before I try again. And while I'll admit that it could be something I'm doing/have done with my tank, I'm also not sure that the LFS isn't just a poor source for inverts. Their tanks aren't the cleanest and they almost always have dead fish somewhere in their tanks. When I tested the water they gave me with the last set, the numbers were a bit off compared to what I'm attempting to maintain.

We're heading out of town this weekend, so I don't plan on doing any additions into the tank until after we get back. At that point, I plan to call/email ReefCleaners.com and place an order for some of the things you've both outlined for me. At this time, I'll avoid any crabs just to keep things simple.

In the meantime, is there anything that I can test for that would explain why snails die so quickly in my tank? Here are my most recent numbers:
77.7F, 1.025, 8.00 pH, 0.014 NH3 (it was 0.004 when I last added the snails), 10.1 dKH (8.4 dKH at the time of the last addition; large water change brought it up), 0 NO2, 10 NO3

 

[LadAShark]

Thanks @LadAShark and @Roboson - really appreciate the continued discussion.

At the moment, every snail I've put into the tank dies near instantaneously. All of them have been purchased from the LFS. The most recent (2 astraea) I drip-acclimated for a bit before adding them in (I now understand that this shouldn't be needed, but the LFS water - 1.015 and 5.8dKH - was pretty different from my water). They were doing okay in 50 LFS/50 my water until the container fell over and dumped all the water out (sigh), so I had to add them into the tank. They were dead within the hour. I considered that they might just be dormant, so I put them into a separate container of tank water and have been watching them for a few days (even did a partial water change with new tank water at one point). They are still limp and haven't moved, so I'm pretty sure they are dead too. I guess I should test the water they are in and confirm (high ammonia should indicate that, I'd think?)...

My tank is still recovering from the first die-off of all the snails I added, so my plan is to wait until my ammonia is back to 0 for a few days before I try again. And while I'll admit that it could be something I'm doing/have done with my tank, I'm also not sure that the LFS isn't just a poor source for inverts. Their tanks aren't the cleanest and they almost always have dead fish somewhere in their tanks. When I tested the water they gave me with the last set, the numbers were a bit off compared to what I'm attempting to maintain.

We're heading out of town this weekend, so I don't plan on doing any additions into the tank until after we get back. At that point, I plan to call/email ReefCleaners.com and place an order for some of the things you've both outlined for me. At this time, I'll avoid any crabs just to keep things simple.

In the meantime, is there anything that I can test for that would explain why snails die so quickly in my tank? Here are my most recent numbers:
77.7F, 1.025, 8.00 pH, 0.014 NH3 (it was 0.004 when I last added the snails), 10.1 dKH (8.4 dKH at the time of the last addition; large water change brought it up), 0 NO2, 10 NO3

While some NO3 is surivivable by snails, any readable value of ammonia is for the most part, not.

 

[DLHDesign]

While some NO3 is surivivable by snails, any readable value of ammonia is for the most part, not.

Makes sense. I'll keep an eye on the number (much easier with the Seneye installed now) and wait for it to zero out before I look to add anything further.

 

[LadAShark]

Makes sense. I'll keep an eye on the number (much easier with the Seneye installed now) and wait for it to zero out before I look to add anything further.

I hope it works out for you.