On this: http://discoverygc.com/forums/index.php?showtopic=17521
(Liberty Navy Ship - Las Vegas) anti-fighter gunboat i had some time ago, i kept enough people to maintain full combat status for one shift. It was not supposed to be in deep incursions, so i didn't require several shifts to be filled. 18 people were enough, including support crewmembers. For a full-time combat gunboat, i'd say about 50 would be required. Even today's small destroyers have a quite large crew.
I honestly think as long as you RP you have a lot of crew, you do not neccesarily require to speak for them all. After all, at most, only comms officer and captain would talk over communications. On broadcast, it would most likely be the captain only. But i consider the bare minimum to keep spaceship crew on board, with maybe some oxygen or something, although you could assume those would be in-built in the ship's life support systems.