Moving up to a larger grow closet suggestions?

I am moving from a very small grow cab from homegrown hydroponics, which has worked well to grow 1 female with DWC over the 2 years or so. I am now a designated caregiver so am planning on a Dark Room model 100 (39.6 inches square and 72 inches tall) with a 3 x 3 foot econogrow ebb and flow system. Hoping to maybe get 6 mature females? would that be reasonable? Planning on a lumitek ballast with a vented reflector. would 600 watts be too much? 400 watts enough?
thanks

im using a 600 watt for 6 plants, they love it. 2x6x8 closet. mixed genetics, 3 dwarf plants(no taller than 24 inches lots of bud filled branches.2 indica's that have reached 42 and 46 inches.1 pure Jamaican sativa*lamb's bread* only time will tell on that ones height.

if you grow heavy yielding lowryder plants(20-25 inches. looks like a giant nugget-no long branches just buds) you can probably get away with 8 to 12 on that setup