Mines in my basement. Whole basement is open but I operate the fish corner. About 10’ long and 8’ wide is comfortable for me to work and set stuff around me.
Biggest recommendation I can make is ventilation.
A fresh air in vent w/filter for skimmer air, air pump air, and fresh air in the room.
Make preparation for a dehumidifier also. You may or may not need one, but better to leave a space, plug, and drain point just incase. Can always set a rubber maid container in its space if not needed.
Power exhaust vent to deal with humidity, co2, and smell. Doesn’t need to be anything more than a bathroom fan. I cannot stress enough the benefits of a air exchange unit if you can swing it. Covers all the ventilation issues with one unit. You can pull fresh temp controlled and filtered air from it and the exhaust will cover the removal of stale air from the room and skimmer if you tap into it.
Small air circulation fan also help with keeping and spilt water and such to dry up quick with no dead air spot in the room.
Proper electrical ran to the room. I prefer a couple individual 20 amp lines or 15 just to distribute the load. Proper lighting so you can see just fine, in cabinet lighting (cheap led tape strips) to make things easier.
Some table top or bench space to work off of. Plus a stool if you find it more comfortable to sit while working/tinkering.
Waterline in and drain line out. I didn’t have a option for a floor drain in my corner so I ran a pvc drain on the wall to the utility tub. My ato and ro water pump up into then run to the tub.
I know most recommend what equipment and skip the stuff that will make the quality of your house and life easier.
Equipment is easy to swap and change. Plumbing, electrical, and venting are usually a easy project if done off the get go, and a bear when trying to integrate after set up.
To me setting up a proper usable fish room is this biggest challenge you can do in this hobby. It takes the most time and planning.
If you plan on running multiple tanks off one sump (I run 3 around my house, soon to be 4) plan for the plumbing on that also. I planned my whole basement set up to handle 1 6 gallon closed top tank in my kitchen. It also handles my 45 in the guest bedroom and 40 in my bedroom. It’s kind of a no brained for remote tanks. All you need for them is light and a water mover and some waterlines.
Just some thoughts for you on the start of the new room.
Keep us posted with pics and ideas! Love seeing what other come up with!