"Most" would be over 60 but then I remove most during veg already. Most I actually vegged till maturity (so I can determine sex) is 35, from reg seed, most males are removed leaving about half, of which I end up flowering 9-16 including 2-3 males that are removed later on.
About 22 left:
That's on 4x4, under 400w hpi-t plus, which is an mh bulb with output similar to the 315cmh but with uv. Nearly all in roughly 0.5 gallon pots.
There's no rule that dictates wattage per plant. That would in any case still depend a lot on how large those plants are.
400watt hps is usually good for 3x3'. You can veg as many plants as you can fit, which depends a lot on the variety you grow and how long you veg as well. With single cola short (afghanica) plants 16 works nice. With taller more stretchy plants a lower amount is more practical.
2x2 is only 4, 3x3 gives 9 plants evenly spread on a square space so when growing for yield that is a common number. I used to do fine sticking to 5 plants though, 1 in the middle.