In order to maximize hashrates we would need to know how much free power you have? You say limited, how limited would determine what miners you could run. How many amps available? 120v or 240v?
Also sound/area/cooling also matters aswell. A lot of these "free electricity" places are apartment's (not all but a lot) and there is limited space so you need to keep in mind mining makes heat and some miners/psu's are loud. So there is a lot to factor in besides just electricity.
I would advise starting with 1 miner see how it goes and then moving up. Some jump in with to many nothing stinks more then dealing with cooling problems, or not having enough electricity.