the galaxy class is not buildable (hey, this class is veeery old, so starfleet won't build new ones if they have the sovereign as a successor), but you can warp in galaxy class starships for your credits.
the defiant class is a short-range battle cruiser, not the weak destroyer it is in armada2
quantum torpedo launchers can fire up to 4 torpedos in a very fast rate but then continue with the normal fire rate. The Federation Sovereign, Excelsior-II and Descent Class ships have Quantum torpedo launchers
btw, all the things above are also implemented in beta1.1 and won't chang in beta2