Hey Andy, That clear cylinder with the bioballs (held by a black clamp and with black bioballs and I believe a black tube coming from the bottom, perhaps going into the clear sump box) could possibly be a CO2 reactor, couldn't it? Its quite common to make or buy CO2 reactors that use bioballs to break up the CO2 gas for greater absorbtion in the water and often this is done at the stage before a sump pump returns the water to the tank. (I don't know, still could be a nitrate filter but CO2 reactor just seemed more common.)
Well, to "mom2", Welcome to TFF. Like the others, I agree that you've got a great "deal" on your hands (assuming the tank holds water) and one of the first things to get out of the way is this question of which path you have "the stomach" for... You sound like you are possibly already willing to take the longer road (possibly more fun!!) and have everyone help you figure out all the sump equipment and then get it all working hopefully. The other road would be the one already mentioned of just basically using the tank and stand and possibly closing up the sump openings in the tank and simply buying and running a couple of large external cannister filters. Its probably important to be aware that you might save many headaches this way, but it would of course likely be more expensive.
I'll bet a lot of the "light switch" looking switches will indeed turn out to be switches for the tank lights and possibly cabinet lights or switches that interrupt the power to the pumps and monitor systems. As for the CO2, I wouldn't be so sure about not doing something with it. Often live plants will be an important part of a big living room display aquarium and CO2 can be one of the key systems to making that successful. If one of the those control boxes turns out to be a device to automatically adjust CO2 flow based on pH, then you may already have the most expensive part of an automated CO2 system taken care of, which would be a real coup.
One thought, and I would hope others would have an opinion, is whether you should try to test the various sub-parts of the system (or maybe the whole thing, however it works out) for leakage while it is still out in the garage. Its kind of hard to know what might leak, either because of breakage or just not knowing what needs to be hooked up and how, at the time of the wet test.
We are already enjoying your photos and I'm sure it would be fun to keep seeing them with the eventual answers to that the parts turn out to be!
~~waterdrop~~