At 3 weeks the stretch should be about done. Get those lights closer if you can, like within a few inches. CFLs won't burn unless they're an inch or closer. She looks a little pale and would definitely benefit from some nutrition. Apply as poster above said.
About 3 weeks from now she'll start having real buds and you'll get an idea of what to expect. From week 6 to 9 she'll probably double the bud weight. She looks healthy to me and if you don't plan on doing much growing there's really not much need to spend money on stuff like pH and ppm meters and whatnot, although you can get cheap ones. Any pH issue and soil can be fixed with crushed lime. Right now I wouldn't worry about it.
Best advice I can give you is to peruse this and other websites and learn from other people's mistakes. Don't buy into every little thing, as there's a lot of groupthink on these boards. Some will claim you must flush before harvest, some say it's BS. Some say add molasses to your soil, some say don't. You should top it, train it, use these kind of nutes, avoid this, add that. You get the point. Do your best and learn as you go. It's really fun and the payoff is pretty sweet. Whatever you do, don't overdo it. When all else fails, leave it the hell alone to do it's thing. Contrary to what some will tell you, you can get some fire ass nugs by literally sticking seed in some soil and watering it every so often, simple as that. And finally, don't listen to the elitist assholes that will try and rip you a new one because you don't do it their way. There's one in every crowd, ya know.
Good luck!
