Welcome. Your little guy is adorable.
I hate to say it, but you will likely need to separate your torts at some point. My two Greeks lived together happily - until one started ramming, biting (causing bleeding), and generally making life horrible for the other. My profile pic was the closest...
I have two Greeks - they cannot be in the same place for more than 30 seconds before one starts biting and ramming the other DO NOT by two, unless you have the room to have two totally separate enclosures.
The mixing tub works great. Keep the substrait moist - mixing in coco coir may help - and humidity should be ok.
As for temps, you'll need to get the MVB higher than the level of the lip of the tub. I suggest either getting a lamp stand or building something, but make it sturdy.