Re: That's not MY ship...!
3-5 is a pretty reasonable loadout for a Federation ship. Any more than that and you're gonna start taking up more space than is necessary. (Tube length and clearance, loading mechanisms and storage magazines. I doubt there's one central magazine - there has to be a decent supply near each tube, I'd imagine.)
STAR TREK: 1964-1965½, 1966-1969, Jan. 21-23 1972, 1979-2001, 2003-2005, 2009-?