For 4 decent sized plants I would go with the larger tent. Use a 400w MH for veg and a 400w HPS for flower. So I would recommend getting a switchable digital ballast. For the fixture, I would use an enclosed air cooled hood(or even a cool tube would work).
For the ventilation a 4" exhaust fan with a passive intake. Two smaller oscillating fans inside to move the air around and promote stronger stems.
This setup should produce some nice buds for you. :jointsmile:

I know that this seems expensive, but we are talking about having a good controlled environment. This is very important.
There are ways to start cheaper, but I think you will find out that over time you will spend more trying to dial in your growing environment if you start cheap.
In my opinion spend a little extra now to save you some later.

If you do run the smaller tent, a 250w digital ballast should do fine. The rest stays the same.

Welcome to the boards, and happy growing. :hippy: