You have a completely botched up plan my man. I don't know if you came up with it on your own but if you didn't if it was someone else who steered you wrong you might want to kick them in the nuts.
You are not going to grow trees in that space with a 1kw light, you don't have the room. You can't veg plants more than 1.5' tall even if they're sitting on the floor because a few feet are used by the light, you'll run out of space. You'll run out of space in every direction in a heartbeat with a 1kw light in there, six plants will have to be trained in some form but I can't think of how at the moment, not quite awake.
When you grow a clone to 18" or whatever it's done vegging and it's going to double in size when flowered.
I understand you wanted the biggest light, but you aren't going to be able to take advatage of it at all until you get a larger space. You can use it, but it's just a 50% waste mostly.
Maybe I'll see this thread later and offer more constructive help when the brain works and I can think of the best way to use that space and that light. You need someone very familiar with 1kw lights and how plants will grow in that space with double the lumens most people use and on hydro. Never having quite attempted what you want I'm not the pro on it, but I can figure it out.