Start by looking in your breaker box and see what size breakers you have. Usually 25 or 35 amp. Each 1000w light will draw less than 10 amps. Digital ballasts will draw less at start up, while magnetic ballasts will surge during start up so I would use digitals if you can afford them. At 10 amps each you can safely put 2 1000w ballasts one each plug in IF everything is in good shape. So trace out which circuits are on separate circuits and wire accordingly. Then you also have to figure in all your other extras like fans or pumps or whatever else you're going to use.
A good way to test if you're drawing too much power on a circuit is to check for heat buildup on the wires. If they warm at all thats not good.