It's normal for the older and bigger leaves to be a little darker green. Don't remove any leaves unless they are blocking the light of buds or future buds, and for some reason you can't tie, bend, or break them out of the way. The plant looks pretty good, except the leaf curl may be from over-watering. You want to let your pots dry out almost completely before each watering. I would get some blue spectrum cfl's and put them in during vegging to help get rid of the sparse stringy look.