no 1000 isnt overkill on 4 plants, have seen 3000 watts used on one large plant before.
if you have a 4 by 4 room would probably try to have atleast 8 females if starting from seed and you would still have room even if you ended up with a 2-3 more female plants than what you originaly planed.
all lights lose intensity at a great rate wich is why you should try to keep the plants as short as possible and just use more plants to fill the space not as easily done when starting from seed instead of using clones, if you was using clones you could run alot more plants up to as many as 3-4 per sq ft in a sog in the same 4 by 4 space.