1. Use the advice of your fixture manufacturer for distance to the light for seedlings, vegetative plants, and flowering plants - each distance could be different. I'm guessing it's more like 24-30" distance for your seedlings.
2. That fixture is probably enough to flower a 3 sq. ft. area but not much more. Based on other feedback on this site you'll see that you will have heat issues as well with it. Just a head's up... for the veg phase I'm sure it's more than good enough.
3. Sativas naturally stretch more than indicas. That strain, per the FastBuds website, is mostly sativa, so much of the stretch is to be expected... however, a good bit of it is also probably due to insufficient lighting. I'm guessing that moving them closer will do the trick.
4. I take the following approach to supporting seedlings, on those occasions I need to (e.g. growing landrace sativas): I cut down plastic straws to size, cut a slit in the side, bend them open and slip them around the stem (taking care not to damage the stem in the process). When transplanting, I bury the stem along with the straw into the new pot, leaving the top of the straw out of the soil so it can be removed later (which I do around the time the stem has thickened to more or less fill the straw). Photo attached.
