1) Where you start out will probably depend a lot on your past standardized test experience. If you got above 750 on SAT verbal, you will probably start out higher than someone who scored in the 600's.
2) Take a course only if you don't think you have the discipline to stick to a practicing schedule yourself. It's not like the courses have some realm of special knowledge that nobody else has.
3) I have found that Reading comp is more of a you-get-it-or-you-don't type thing, while logic games can be learned fairly easily. Logical reasoning can be learned too, but it takes much longer than logic games. I'm finally getting to where I can consistently miss 2 or less questions per LR section, but to get to that point I had to do about 1200 of them.