Dont buy a MH, they're only good for veg. Buy an HPS if you're only going to buy one lamp. Buy it ready, if you're not good at electric. there are massive sales on the internet, E bay, now and again.

Forget the co2, thats for pros and demands real equipment.

Good soil and perlite 50/50, proper nutes, temps between 25-30C at the canopy top, and you're good to go.