I have done 4, 3, and 2 in that space. Well it is a 5' x 2' closet but I utilize a 3' x 2' area for the grow with my 400. 400 can cover a 3'x3' area pretty well. Any combo will work and fill up that space just depends on how you want to grow, how long you veg, technique, etc. more is not always better and you have to consider heat, air movement etc. I would start with two for your first grow in this area and see how it goes. By the way I harvested the same with 3 as 4 and my 2 plants growing now I topped and lst and hoping to get similar results which would be 6 oz. there is a good journal will see if I can find it guy in similar setup with 400 and two plants produced 5 oz per plant! Just got to dial in your space and find what works best for your setup. How much height you got?