OK, I like the idea. However...
This is just my opinion, and I am not taking a contrarian view, I just want to put some things out there. If we are to do this, with hopes of educating and generating interest, I don't think it can be somebody's old 55 gallon, with a worn pine stand. From an exterior view, this thing has got to be very attractive. Yeah, used Metal Halide ballasts, and used sumps, and used pumps are ok, as they are out of site generally. But the part that the viewer sees, the part that makes the someone go "Wow!", has got to be first rate.
Also, think about the space you are putting it in. A 75g in a 12'x14' living room is a nice size tank. Put that same tank in a hall at the Art Museum for instance, something that might measure 35' square, and a 75g is waaaaay too small to make any kind of impression. My thinking is that a 180g would be minimum for a large room, and 3-, 4-, or 500-hundred gallon tank would be more appropriate.
300 is a lot of water, power, maintenance. I we can find a host that is willing to cover the electricity, and a tank builder willing to discount or donate a 300, same for a cabinet builder, and we can get commitments from members for frags, we still have to buy the fish. Like most, I don't have any spare fish lying around, so we would likely have to buy them, especially if we want to control the temperament of the tank. If somebody donates a clown trigger and someone else an ocellaris, we are gonna have a problem.
Now on to staffing. We will need a tank master/project lead/CEO. Someone who is willing to make the final decision, and we would all allow to make the final decision on everything. Otherwise, nothing would get done. We need fund raisers, and sponsors. We need an advisory and planning board, led by the tank master. We need maintenance staff that would be willing to do chores and respond to emergencies. If we are to educate, we need a trainer. None of these jobs are particularly huge, but they ALL will need to be done.