Yeah all BMs eventually break in as coxswain, and at chief or SC usually get their first command of a unit, generally a 20-30 man small boat station, I heard the Navy requires an officer on all vessels, even something like a small RHIB, the CG doesn't have the manpower gor that. I was a coxswain on a 27', one of the prototypes for the 25' fast boats the coast guard uses everywhere now snd the 41' mlb, which were just a bathtub of a workboat, usually a 3-5 man crew underway.
I should have gone to a Maritime academy, would have saved a lot of headaches. Definitely the way to go, and I think taking the reserve commission is a good idea too, my uncle did it. He retired as chief engineer a few years back. Great job, good luck