Personally I'd build a growing cabinet for less $$$ than it takes to buy and ship a grow tent. I like my enclosures SOLID.

In a 4x4 area, minimum you want is 600w if you're going with HID. If you went LED, you'd want minimum 300w.

Soil is the best for starters, unless you have experience maintaining pools and aquariums, in which case I'd recommend hydroponics since you've got half of the required maintenance stuff already in your head/practiced and the rest is not too much of an issue at all.

But you say you're doing 3x3 area, so 240w LED or 400w HPS would be the minimum I'd recommend. Make sure you line the box well with a reflective material. If you can't do that, eggshell white paint is the next best substitute, or silver/chrome spraypaint that is evenly applied can work better.