But I would need to buy a carbon filter and the extras, right?
I don’t like to make sweeping generalizations because the cannabis genome includes a wide variety of morphological. But it’s possible to keep a cultivar like Blackberry Kush in a 1’x1’ footprint. Ignoring autoflowering cultivars, you can fill an entire 6’x6’ tent with one plant, but I wouldn’t.
I feel like 1 plant per 2’x2’ footprint is right. You want the tallest tent you can get though. That’ll help you fit humidifiers, heaters, and anything else you need. Headroom is precious.
I have a 2’x2’ box. You can see it in my threads. If I could take up more space in my brother’s garage, I would. Look at the cost of a 600w HPS and a 4’x4’ tent and compare that to other options.
A grower will need to buy a ventilation fan for any tent, and I cannot imagine not buying a carbon filter along with that.