optimal lumens per square foot

The closet I'm growing in is 3'x3'x8' but since I only plan on growing two Northern Lights to four feet + one foot for the pot + one foor the light should I theoretically calculate the square footage by 3 x 6? I've read that 3000 lumens psf is optimal so 3000 x 18 would be 54000.

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

This shoots out 58000 lumens.

I also have another question. If I get that light I will be getting this ballast

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

or this

http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW

which would you suggest I get? I have a budget of 300 for all my supplies so I'm trying to keep it relatively cheap. The rest of the majority of the money I plan on getting for fertilizers. I'm still not sure which. I might go with what someone does at overgrow (BOG last post of page) but that's a lot of different fertilizers. I might also go with all bio bizz products if I can find a decent paypal site.

I also have a question about watering. If I'm supposed to put like 1/2 - 1 tablespoon per gallon how do I go about doing this? Do I fill a bucket of water with a gallon or so and dilute the mixture and then feed it to the plant over the course of the week or will I be feeding like a whole gallon to the plant every other day? I really don't understand.

Thank you.