I would put 2 600W lights. I aim for 35W to 40W per square foot because that kind of footprint is a good balance between heat and plant performance. 2 600W in your set up would give you about 38.7W per square foot.
As far as number of plants? The more the better in my opinion because more plants equals less veg time. If I had enough clones I would do a flood drain table and pack at least 60 clones and switch them to flower as soon as they rooted.
If I didn't have a lot of clones to do a sog I would grow in coco using smart pots. 8 - 5 gallon smart pots (4 week veg with a good scrog) or 20 - 2 gallon smart pots with a 2 week veg.
Whatever you go with, i highly recommend you use short and wide pots with 6ft height and 1kw. Thats 4ft left after a 7g pot and a hood meaning you would be cutting it close if you were to be flipping plants at 24" in that example.