Welcome to Reef2Reef and to saltwater!
#Welcome to reef2reef!
Solid choice on any of the IM desktop tanks, any that you have the space or budget for, go for it; they are great tanks! If you have the room, the 25 lagon is a great tank
The IM's are a great kit, but either buy the "pro" version, or plan on upgrading the return pump sooner than later. Popular choices include inexpensive Sicce pumps to the Innovative Marine Might Jet DC controllable pumps and others. Jebao makes an inexpensive Chinese knock off of the IM Mighty Jet. I have several of both, the Jebaos are just as good as the IM's, I'd look at those
First decide on a live rock vs. dry rock start, both have advantages and disadvantages; you'll want to choose your path now.
It all starts with saltwater, and best practice is to have your own RODI system to make purified water to use to mix saltwater, and to top off evaporation from the system. If you don't have an RODI, you can purchase gallons of distilled water from any local grocery store, pharmacy or your local Mega-Lo-Mart fo about $1.50/gallon. Use this to make your saltwater and to replace evap. Last, you can often buy RODI and/or premixed saltwater from your LFS, but double check their parameters before using, don't just assume they are perfect because it's the fish store's water.
You need a salinity tester of some kind. Use this guide to calibrate it using a simple to make DIY calibration solution. If you have questions, just ask!
https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/
To get your tank going:
For dry rock, use any bagged sand, 'live' or not, and a decent dry rock such as Marco Rocks, Caribbsea South Seas Rocks (white) or Caribbsea "life Rocks", if you like the color and price tag
You need to cycle your tank with dry rock and sand, you need a source of bacteria and a source of ammonia. I'd suggest Fritz Turbostart 900 and Fritz Fishless fuel; other methods are available too, but Fritz is by fay the quickest of the bottled bacteria products.
You're going to want a decent test kit for ammonia when cycling; Salifert is the suggested test kit brand. You'll need nitrate at this time, and go ahead and pick up phosphate kit now or in the next couple weeks. You can ignore "master kits" with pH and nitrite; those are unnecessary to test for most hobbyists. Things like Alk, Calc, Mag and others can wait until they are needed (if ever).
Now, if you you can afford it, take a look at the live sand and rock packages from Tampa Bay Saltwater, this is the premium option

Your tank will be 'instantly cycled', an you'll receive and untold number of critters and hitchhikers, it's amazing. Yes, you may get some pest hitchhikers, but they can be easy to deal with. If you can fill your whole tank with TBS rock and sand, consider ordering at least a few pounds of each. This will go a long way to 'seeding" the rest of the tank with beneficial microbes.
Behold!
https://tbsaltwater.com/collections/treasure-chests
IF you can't swing TBS rock, see if a local fish store has some good live rock.
I'd get a decent quality heater and a heater controller, which is like an emergency backup switch when - not if - your heater freezes in the 'on' position, resulting in a seafood boil
You're going to need an Auto Top Off unit. Don't try to skimp on this, an ATO goes a long way to maintaining a stable salinity, which is important to coral health, especially in smaller systems. But, topping off manually every day gets old, FAST, so an ATO goes a long way to maintaining stable sanity
You'll need lighting if you want to keep corals; that's going to depend on what you want to keep and what tank you ultimately purchase.
When it comes time to add fish and livestock, I'd consider quarantining your own, or purchasing livestock from vendors who specialize in pre QT'd fish and livestock.
If you're brand new, I'd suggest this guide:
https://www.reef2reef.com/threads/the-supreme-guide-to-setting-up-a-saltwater-reef-aquarium.138750/
As well as this video series:
https://www.bulkreefsupply.com/cont...wabUoMI8zq3C3sZnAXE1lO6yd0vR7xW2yRnRhCrecwd9X
I hope this helps and good luck with your build!