If you want to flower 20 plants at the same time, you will need a lot more than 2x400W lights. Flower under that combo with 20 plants, and you'll yield as much as you should have growing 3 or 4 under a 400W. If I were you, I'd get 2x1000W for that number of of flowering plants, at the minimum. For your clones/veg/mothers, invest in some CFLs, much cheaper than MH and when used correctly, will keep your youngn's very short and stout.

Also, I'd lay off the nutes for another week, they're still too young for that. It's probably why the leaves are curling. Good luck!