Sugar? I have never heard of that. As far as watering goes I tend to underwater rather than over water. If I see the leaves sagging I know its time to give that thing some water and it perks right back up within an hour. You dont want mold or root rot. Make sure you put some quarter size hols in the side of the box for cross ventalation. If you can get Mylar it is much better than tin foil. Tin foil believe it or not is pretty low as far as reflectivity goes and is a big conductor of heat. So that box might get as hot as 90+ farenheit especially with those UV bulbs. How many Lumens are those bulbs? If under 1600 go get some compact Fluoros. If you have the money get a ballast and a Metal Halide bulb. Mylar is about 10 bucks for 10 yards.

As far as the watering goes you will get a feel for your plant. Just remember under water is far better than over water. If you feel your plant looks poorly dont fear just water it and youll see itll be as happy as you will be during harvest. Good Luck and I hope I helped.