BDCP is a Navy only program. You get paid at the rate of E-3 for up to 36 months before graduation (36 for technical degree, 24 for non-technical degree). You then owe the Navy at least 4 years active, 8 years total (some designators are more). If you drop out of BDCP, you will serve 24 months enlisted. When you apply, you give up to 3 choices for designator, and then you are accepted or rejected for those designators. If you are accepted by more than one, you will pick one. Assuming you don't fail out of the training, that will be your job in the Navy.
There is a lot of good information is this forum about BDCP. I would also recommend talking to an officer recruiter -
www.navy.com can give you a phone number to call.