First of all ! Or should I say, welcome back!

I think your plan sounds pretty good, though I'm curious as to how you would use the IKEA Pax system with tubs. Its an interesting idea, but I'm not sure how well it would work. You might just be better off buying a small "sideways" rack. One that can use 2 15qt tubs per shelf or one 32qt tub per shelf so you can house adults and babies together.

I would also recommend a thermostat instead of a rheostat. A rheostat is going to require constant adjusting (which is annoying) where as a herpstat will keep the temps steadier.