With regards to the housing situation, it completely depends on where you're stationed for UPT. At Laughlin they're currently pushing pretty hard to get every unmarried Lt into the dorms. So, if you show up for UPT here, expect to be forced to live in the dorms. The only exception is if you show up with a large influx of Lt's and they run out of dorms rooms- in which case they will sometimes allow you to live off base or live in base housing (sharing a duplex with other students). If you are married then obviously you're in the clear and won't be pushed to the dorms.
The point is that if you live in the dorms, you don't get any BAH. If you live off base, OR if you live in the base housing with roommates, you get the seven hundred something bucks a month. Bottom line is be flexible.