You could probably get away with two lights. Three will certainly saturate the space. Using scrog method it is usually recommended that you give at least 1 square foot / plant. However, I found that to be small. Of course it depends on how long you veg the plants and the stretch associated with your strain. You could grow 24 plants in that space if you keep the veg time to a week... Don't forget that you will need room to move around in the tent so that you can access the plants. You need to do the training and pruning not to mention watering and feeding. I would do U shape setup with a work space in the middle of the U. You can probably get 12 plants in there but 8 - 10 would be more comfortable. If you start with 12 then be prepared to cull a few to make space if needed, although this is difficult with scrog. Perhaps you could lay it out, build your screen and then use 1 foot and 2 foot squares of cardboard to see what will fit. The problem with scrog is that under estimating space requirements results in a seriously overgrown garden which of course pushes down yield. Yield is dependent on so many factors - the plant, how big it is allowed to grow, skill of the gardener, feeding regime, etc.