One of my bro's does real good with a 250 hps. If you want to use the light for both I would look at the new horitlux blue bulb. It has way more blue for veg and way more red for flower in it's spectrum. 2x4/5 it depends on the system you run. I could just fit 3 ten gallon tubs in there with either 4 / 5inch netpots or 6 / 3 inch netpots in each tub. That's 18 and you would get about 2 foot plants in the 6 foot tall room. They would be bubblers or dwc mostly the same thing.

Heat will be your main enemy in that space. The water need to stay around 70 degrees. The strain is up to you, northern lights, whitewidow, lowryder. I go with the most potent and short flower period.