Here's my two cents,
1. Stands - I'm looking at industrial racks, probably Galdiator, Husky, Kobalt, etc.
I've been using a husky stand with 4 x 40 gallons for four years with no issues. Did cut a nice piece of plywood to act as the shelves to spread the weight. I also have built two wooden racks and two block stands. Metal shelf was easier and looks the nicest. All of them take some work/time but no real upkeep.
2. Tanks - mostly 20 highs and 10s but I might bring some 40s with. Tanks will be positioned short side out to fit more. Final count around 40-60 tanks.
20 longs make more sense than highs..especially if 20 highs are on top shelf. Netting fish and stuff out of those tanks is not fun. Longs provide more space for the fish to spread out thereby reducing stress.
3. Lids - Probably polycarbonate +/- a hinge.
Feeding hole can also be the finger pull to get the lid off. Open tanks are losing heat. Though the green house plastic is cheaper.
4. Water - EXTREMELY hard. Auto water change? Continue with manual water changes?
Money and time, do you want to spend more or less? Hard water also means potential issues with calcium build up. Keep in mind too, all of those can be done in stages.
5. Lighting - I currently run cheaper aquarium lights, one light over 3-4 tanks. I've been trying the Co-Op light and will probably replace the cheap lights as they die.
If you're not doing plants, don't bother with lighting every tank and instead have a mobile light.
6. Heating - I have been heating the current room and had partially settled on an oil radiator heater for the new room. If a do a central sump system, I could in theory heat the room less and put heaters into the sump.
I have two oil radiator heaters running and they pop up your energy bill. But I also have a large basement and keeping the room even 72 degrees is a challenge. IF you come up with something better, let us know.
8. Filtration - A part of me is tempted to just continue with the sponge filters and just keep up with everything manually, it just takes so much time though. The other part of me is seriously tempted to create central sumps, say one for each rack. I do quarantine but having multiple tanks on one system would be new for me in my own fishroom. What makes sense with this many tanks?
Air ran filters is cheaper than pumps. Matten filters can go longer without cleaning. Plus, press your water vaccum into the sponge filter and it'll pull a lot of gunk without .
9. Opinions - Manual water change vs auto water change vs central sump? What would you change? What would you add? What did you wish you knew when setting up a fishroom?
Go in stages to figure out what does and doesn't bother you for adding on to the room. That away too, if you hit a point of too many tanks, you'll have a better idea of what size you like.
Mentally prepare a schedule to maintain each rack. Couple hours a weekend day is better than a whole day/weekend once a month.
IF you have a yard/garden, drain your water out there and save on fertilizer. Plus, less potential to clog up a drain pipe with snails.