Newbie need experienced advice for first grow on equipment

That particular light is a bit older or using older chips with the cree cobs. Cxb3590s ran at 100w each is a bit high. I have some of the same chips in my old DIYs at 50w and 75w. They were very good chips about a decade ago. This light will make a bit more heat than the newer osram/samsungs. 800w is a good bit; in a 4x4 I'd probably never turn it above 75% power unless your supplementing. Of course you want to check it yourself with a par meter/photon app. The hang height with 120 degree reflectors should be about 12-18 inches above the canopy, but again, check the par. Overall not as nice as the bar style or board style lights, will create more heat on your tent, and require about 30% more power for the same light output as the newer around /watt lights out now. For about 400(.50/watt) bucks brand new, it's priced appropriately. If youre asking how many plants for that space, Id say its entirely up to you. Ive seen a single well trained plant fill a 4x4 space nicely, and Ive seen 48 plants SoG style. Most commonly, I think you want 4-9 in there.