sounds perfect actually but just make sure that you have a way to deal with the heat cause there will be alot of it. My suggestion is using a cool tube.
Yep, sounds good man- You'll be really good on lumens for 9 feet square.
I've got a slightly smaller area than that (8) and use a 1000w HPS in flowering for 5 females, with lots of space. Just make sure to get a good vented hood and be sure to keep the temp down.
Your grow area is only 4 feet tall? Might be a problem there.