Sounds like you are on the right path, definitely beef up your electrical for power, before worrying about how much power a sub will handle.. throwing tons of power on sub with stock electrical a bad thing. You'll start dipping in lower voltage clipping crap out of amp..which will lead to broken sub and amp.
You could shoot for a bigger amp when ready, so you won't need to rebuy later, but you would need set your gains low side . Keep in mind 750 watts to 1200 watts is really not much of a gain . You'll just set lower gain, not as much out out.its all about knowing the sub and amp what to listen for when playing music etc etc.