It's not about less light, it's about the area covered. 1 600w light covers an area about 4ft x 4 ft. If you can fit all your plants in that area, do so until they outgrow that footprint then turn a second light on and spread them out a bit. Remember, lit floor is wasted electric.
24 WW plants will fill that room well. They stretch about 2X. Are they feminised? If not, no matter. I would aim for about 16 fems (4 per 600w light). Grow until each is 1ft across (so, ideally, you would need a 4x4 veg cab and a 600w) then extend or shorten your veg time to compensate. In an ideal world, you will get 16 fems which will grow to 2 ft across each and fill your space perfectly. If all 24 are female and germinate, veg about 3 weeks (after first true leaves), if only half are fems, veg around 5 weeks. Just remember you are aiming for a full canopy hence the most efficiency.