If you don't plan on using a carbon filter that's your choice but an extraction fan with a fan speed control is pretty important to remove excess humidity especially during flower time where high humidity can bring on bud rot. Along with that a small inline fan replacing the air that was removed by your extraction fan.

Lights? Save your money and do your homework cause there is a ton to choose from.

In a 4x4 tent properly set up you can grow up to 4 medium plants but your light needs to be good enough to penetrate Thru your canopy.