Definitely give them distilled water if possible. It's only 78c per gallon at Wal Mart. Do you have one nearby? Well water is still prob better than tap water. Don't feel bad about using CFL's. I don't have an HPS at the moment either. Just grab 400w off htgsupply for about $120 as soon as you get the chance. That's what I'm planning after I finish my current grow.
You can use small amounts of sodium bicarbonate (baking soda) to raise the PH if it's too low or acetic acid (vinegar) to lower it if it's too high. They have ph pool test kits at wal mart in lawn & garden for about $5.95 too. They're pretty good for testing the water.
The only thing I'd be worried about in the compact space you're using atm is heat. As long as you can keep your temp in the lower 80's or late 70's you should be good.
A little bit of yellowing on the bottom leaves is normal with Miracle Grow. Eventually, some of them may fall off but it's nothing to be concerned about. As far as watering goes, only give them water when they ask for it. They'll get a little droopy when they need it and the soil will be pretty dry.
They look really good though dude!