Hard to say man, depends on container size, and size of reflector hood.
My friend has the Sunsoaker hood with 1000 watts and puts 20- 24 clones under it with a 3-4 week veg time Sog style. Works well with an average 2 1/2 lbs per harvest.
I have tried 24/0 and it does not seem to help the plants grow any faster.
I also keep mine on 18/6 to cut down on power costs and it is widely believed that plants use the night time to establish roots.
Miracle Grow will destroy your soil over time.
Each year you will have to add more and more MG to get the same results and in turn you will be adding salt that will kill any beneficial microbes in the soil.
MG is BAD.
I set my dehumidifier to 35% but forget to empty it sometimes and it can reach 45-50% with no problems.
Just don't want it to be super humid or you will have problems with bud rot and what not. :)