90 amp alternator. Add up all the power sources and make sure it stays under. Keep in mind sub numbers usually refer to 'peak' watt performance, not RMS. A 1200 watt sub won't be constantly draining 1200 watts.
That being said, I have H4 headlights, fogs, KC slimlights, GPS, phone charging, and 700 watt sub and don't notice any dimming... My previous vehicle would tho. I always thought it was entertaining.