The power system itself would be fine; after all, T2 generators put out 500 MW each, so having a large ship with 5+ GW power generation wouldn't be hard to do. Having energy turrets consume 100-200 MW would let you mount 10-20 of them without much problem. Would you want to turn them off when you weren't using them? Yes, of course (that's what happens in Star Trek, after all). The real problem is the fuel system; it was clearly not designed with scaleability in mind. A secondary problem is the thrusters, which don't draw nearly the power they should (their power consumption is about a factor of 10 too small), and the fact that there is no easy way to cruise without consuming power once your ship is up to speed (aside from manually turning off thrusters from the power panel).