i am dealing with almost the exact same room except my roof slope stops halfway down, you could definitely throw in a 600 w and gorw 6 plants with good ventilation
if you have good ventilation and the room is not split in half(veg/flower) you can probably get away with that if you have an air cooled hood
I would start with 8 to 10 plants and cut 2-4 of the smallest plants out two three weeks into flowering, leaving you with some larger 6 plants the 1000 will be able to handle foliage penetration. you could sog say 10-14 smaller genetic plants but would recommend a light mover