Sounds good and you have done some homework. I like that.

If your buget allows. Get the biggest ballast you can and a switchable ballast. Then you can get the biggest HPS bulb you can. Then a MH bulb to go with it.

This is how I set up my bro. He has a 600 watt ballast switchable. He runs a 400 hortilux HPS for flower and a 250 MH I got from slowe's for 25 bucks for veg time. He just switches when it comes to flower time.

One plant is like I told my bro, putting all your eggs in one basket but he has done pretty good like that from clones.

The point of having a large ballast is you can run smaller bulbs in a big ballast but not the other way around. Big bulb in small ballast blows up I have done it and I'm an electriction. Then down the road you can always go bigger once you see how it goes for you. Just get a bigger bulb.

Search around there are some good deals on the net. If you can't find a good one tell us your budget and we will help find something for you.