vegging = when you grow the plant with a light cycle of more than 14 hours making the plant grow fast and hearty before switching the light cycle for flowering.
Co2 = do some reading on this, there is AMPLE info out there for Co2 feeding.
I grow kush myself, good choice. You only have the 1000 watt eh you may wanna just stick one more bucket (6 plants) in there and only veg them for 2 - 3 weeks. You will get 12 smaller plants that produce a crop fast... like 10-11 weeks total time, have fun