I'm curious how many plants can grow under one 400w MH system. I intend to get more and use a light mover but to be accurate in plant spacing and amount I want to make sure I don't go overboard. The suggested grow area for a 400w is 4x4. With hydroponics only taking up a small amount of space that could amount to 16 plants if 1 sq. ft. is taken per plant but is that overkill? Here are some basic questions then I guess.

How many tomatoes could grow under that light?
Peppers? Cukes? A mix of the three?

I just want to make sure that when I grow the plants I don't overcrowd. Thanks for the help.