Tried it once...we used a Rigel-class scout, crew of about 40 plus...it was like one of those WWII submarine movies. Small crew working in a very small ship...it was a good starting point for a new group as it'll teach them to work together.
With regard to CO rank, I think that any ship smaller than size 6 should be commanded by a Commander...and anything under 4 just needs an senior officer (lieutenant or lieutenant(jg))...just remember except for shuttles and runabouts any ship CO is still called "Captain" regardless of rank.
Arise, arise, Riders of Theoden!
Fell deed awake: fire and slaughter!
Spear shall be shaken, shields be splintered,
a sword-day, a red-day, ere the sun rises!
Ride now, ride now! Ride to Gondor!
Theoden King: The Return of the King