question about Bah (not enlisted yet)

so I haven't entered the military yet, what should I ask about bah and bas when I get recruited?

so instead of using bah to pay off a house, could I use my possible bah pay for cheap rent and then keep the rest when I leave.. same with bas.. is that how it culd go about it?.. I think If I use it for mortgage it'll come up to nearly the same amount as buying it out of pocket and I imagine the house will have issues overtime if I enlist long enough anyways?