Greetings....As I'm sure you know, the CG merged the QM and BM ratings some time back, so now there's just BM. In order to determine what rate you'll come in at, your recruiter will prepare what's called a Rate Determination Package. This is a package containing all your relevant rating specific training and other education, and is sent to the BM Rating Force Master Chief (RFMC). The RFMC will review the package and then make a determination as to what rate you'll be brought in at. As M1a said, it's possible you may get bumped back to PO3.
To get your conditional release, your recruiter will provide you with the DD-368, which your current Command will have to sign off on.
As for getting co-located, it can certainly happen, but know that the CG doesn't have nearly the number of large bases that the USN does. There are, however, a good number of small boat stations that are miles from any other military installation. If you're seriously thinking about the CG, you and your spouse need to have a real discussion about the possibility of being Geo-bachelors.