Im a 2 part noobie, but I do know some answers
1) too many out there man...
2) yes and yes. Some people mix their own colors with clear, some paints come premixed.
3) Yes, just expect to put on a few coats to get proper build. It doesnt "soak in" like nitro, so it will be more stable. If you apply it thin enough, yeah you can see some grain.
4) MUCH quicker. faster curing = faster to cut/buff the guitar and get it finished! Also means you can add more coats faster.
Ill add, nitro is super flammable, its caustic, and isn't a particularly protective or stable finish (temperature affects it a LOT, very soft on a hot day, very brittle on a cold day, etc).
The flip side, most 2 part paints are absolutely evil, and contain every known carcinogen known to man haha.