Lessons with a good teacher is very helpful.
Also check out
Learn how to play guitar and order the DVD & book and make sure your teacher understands the materials presented in them.
William Kanengiser has some great learning videos as well - this is a tiny sample:
The fingernails don't have to be very long at all, mine are only a tiny bit longer than my fingertips and don't affect electric playing very much.
How long it takes you to get good at it is entirely up to you, and trying to aim for any specific amount of time is meaningless in my opinion. Like any other skill, it takes regular and frequent practice. I'm sure you'll find that practicing classical guitar will improve your electric playing and overall musicianship tremendously. Best of luck
