I should have said im growing tomatos which i am. Ill also say there harder to grow from what ive researched. So ya you should be ok in your closet for sure.
your fine, 2x is basic 3x and you can do 4 plants in a 3x3. I do 4 and they are pretty big, if I did one id have to give it a super cape. and 400w hps is def gonna do the job decent. You should have some kind of ventilation though, if no proper setup then get a BIG FAN and crank it like a foot...
buy a tent :shock::hump: it would save you so much trouble, for example I have a dr90 secret jardin. Cost me 220$ and its super easy to use, plus it goes with me where ever I go.