The RO wash should purge any last remaining chlorine.I've found this thread right on time, thanks @brandon429 for putting all this together. Amazing work!
I have a 30 gallon tank which I'll be taking apart to re-do the plumbing and aquascape. I will for sure be cleaning the sand as you mentioned. I was religiously told to not use the old but now I understand why. I had a question about bacteria dio-off from washing the sand in tap water with has chlorine in it. My initial thought was that before the last rince with RO water, to do one last rince with a water primer to neutralize any chlorine left. Would you say this is ok to do or skip it?
As for the 20 or so pounds of marco rocks in the tank. Should I clean them with a brush in tank salt water before plating it back in the DT, and will you suggest using Dr Tim one and only to seed the tank a bit more or will the 20 pounds of live rock and porous media in the sump be enough?
If you're really worried about it, during your RO rinse add 10mg crushed/powdered ascorbic acid (i.e. Vitamin C) per gallon of water, which will safely breakdown chlorine without harming anything else whatsoever.
Personally, if you're looking to keep your biodiversity, etc., I wouldn't scrub the rocks unless they're badly covered in algae or some other nuisance. Otherwise, I would just put them in a bucket with tank water and shake a bit just to remove any loose detritus.
As for Dr Tim's, why? As long as you keep the filter media from the old tank submerged, THAT is where the vast majority of your nitrifying bacteria will be.
Just don't change the filters. Rinse them gently in tank water if you need to shake off any excess schmutz, then keep them wet. If there's not going to be any fish in the system for some time (for whatever reason) then you might want some ammonium chloride to add in small amounts to help keep the bacteria fed, but otherwise, yeah that chunk of liverock and filter media in your sump will be plenty enough to keep the cycle going.