On sngs/tourneys vs. ring games thats really a personal decision. I play cash for the most part and I have been doing pretty decent so far. It really just depends on what you want to do.

On pokerstars vs. tilt, I've heard that Tilt is more of a nitfest then pokerstars. If you decide to switch to cash I would switch to pokerstars just because there is more traffic.

Go to the beginners circle and look in the "beginners digest" thread
Lots of really good info for someone just starting the grind.

Good luck!