In Fleet there are two Starship Upgrade vendors, one for credits, one for commendations - both are standing right next to each other.

You can also buy single-use "Fleet Pass"es which work like your emergency fleet pass (but consumable) for 1000 credits in fleet (security vendor, I think).

I haven't found one on the Promenade - guessing there isn't one?

Not yet.

It auto-casts whatever is in the first slot of your primary bar. Have you tried not putting anything in that slot? Beyond that I don't know of any way to disable it via preferences.

You should get several (~4) daily flight missions from the comm on your ship. These almost always give you quite a few more commendations (like 4-5). You should easily be able to earn a dozen or more commendations a day from doing your dailies, which puts you into the 300 range in less than a month.

I have the "Apprentice" title, but never received the Acolyte title (I am a Sith Inquisitor). is there something I need to do to unlock it?