I have a 3x3 ACI tent and a 4" ACI exhaust fan. I have had the tent a couple of years now. On retrospect these are the things I would do different.
I would not do a 3x3 again, the cheap light options are better for a 2x4. As others have noted it needs to be at least 6 ft high. I would definitely go with the ACI brand for the tent and exhaust fan. The tent fabric, cost and the control plate make it a winner over Gorilla. I like the Viparspectra lights as having good bang for the buck, two Xs1500 would be ideal for a 4x2 but there are many good options out there. Definitely shop around for the carbon filter there are cheaper options than ACI. For a circulating fan do not be seduced by the hype over the ACI fan, it has the same plastic gears as the rest of the cheap oscillating fans. I wouldn't buy a kit, not worth the extra money for the convenience plus you are limited to one brand for all the components. If I did buy a kit I would go with ACI. If you go with soil be careful you don't have gnats! Pro-mix is where it's at for soil grows, you can get a compressed brick at walmart for 13 bucks. I tried miracle grow, miracle grow organic, black gold and ocean forest, all had gnats, only the pro-mix was gnat free.