how many plants to grow?

im starting with seeds using http://www.htgsupply.com/viewproduct...roductID=53519 as my hydro system. im running a 400 w mh than switching over to hps. im not using two rooms for veg and flowering just one. so... what are some opinions on how many plants i can grow?

thanks guys

p.s. its white widow if that changes anything

more than one for sure. id do 3-6

one every other slot