I guess it depends on how you grow....I run two now plants and can fill up that entire space.
View attachment 2744773View attachment 2744774
I have done 6, 4, 3 in that space, I was just thinking if it is vertical grow with no cool tube the light would need to be hanging higher over the plants as opposed to in the middle more at the plant level. Otherwise he only has a foot or so on each side. Anyway, sure he will figure it out as he goes
Also regarding the two lights.....two 150 hps is going to run cooler than one 400 and you are starting in a cool space which helps as well. Trial and error, like everything on this board you will get lots of different advice and none is going to be perfect for your area because everyone has unique situations.
I am sure you have checked out the vertical grow section on this board....lots of good stuff!