You know, I should post a thread on where and how to start modding. You're asking the right questions, but there is more to it.
The reason you busted a spring is because they probabaly weren't the right ones for your set up. So here is the first question you have to answer. Do you want to lower the car for the sole purpose of lowering the car or for performance upgrades and better handling?
For just lowering the car, then you can get away with just springs, but remember that they work together with your shocks. Teniko and Tanabe are the best spring kits I've seen. I have installed Tanabe's before. The ride itself was a little stiffer, but otherwise not to bad.
But, in my opinion, if your gonna do it, do it right and go with coilover's. I lowered mine 1 inch in the front and 1 1/2 in the rear to level it. The ride is actually better than stock. It's for one quieter. Yes, I said quieter. The Tein coilovers and GReddy's have a better bushing system that help keep the road noise out. Also when I go thru high speed sweepers, the car is way more stable, no floating or body roll. Also, because the shock and the spring are tuned to work with each other, they respond to bumps in the raod much quicker, keeping the tire firmly planted on the road. So the ride is actually better, And with preload, rebound and damping adjustments, I can tune the suspension to how I drive. If you do alot of adjusting though, you might want to look into a camber kit also, but I found that unless your racing, you don't need one. You can install them yourself easily, but expect to pay around a grand for a good set.