you could prob get 6-8 plants in there. depends on your style. lots of little plants or less bigger plants. how do you plan on growing them anyways? SOG, Scrog, or Au Naturel? nutes? soil er hydro? so many parameters so little info from you. best of luck!
I got one of these tents and its totally worthless. 400w at most but I'd recommend only 150 or 250. Its not really worth the electricity for the floor space to even use the 20x36 thing unless you use fluorescent and veg.