Hey Ryan you're welcome to come check out my fish room if you're looking for ideas. Pretty similar in some ways.
A couple things I'll point out:
- You'll want the room sealed from the rest of the house to prevent moisture spreading
- You'll want some kind of water resistant layer to prevent mold growth
- You'll want humidity control, I wouldn't use a bathroom fan 24/7, it probably won't last long plus not very efficient.
- 90 gallon grow out tank would still probably be better suited as a low tank similar to frag tank, don't see the need for a 24" tank unless you plan on growing corals 24" tall. Actually don't really see the need for a grow out tank and a frag tank but you probably have different plans than most hobbyists?
- I'd make better use of the space with racks, stacking tanks three tall instead of 2.