Start small, as in 1 or 2 GPUs. It's easy to add more later. It helps to have the machine be multi purpose so paying back the entire cost would merely be a bonus.
That sounds like the smart move. As someone mentioned above ... Two GPU's in a computer case isn't going to scream "MINER" to the university or a roommate. As far as the network goes, just use a mifi or some sort of cellular hotspot instead of the university network. The data useage will be minimal.