1) Yes, you can build your roll from just ring games. I have, and so have many others. Ring games are generally more profitable than tournaments. If you want some examples of people building their roll playing ring games, check out this thread.
Most of those players are playing ring games.
2) Yes, you should have at least 20-30 times the maximum buy-in in your bankroll to play ring games. So if you're playing $0.01-$0.02 No Limit, then you'd need at least 40 dollars in your bankroll.
3) Don't quit, learn & get smarter. Poker is just like scrabble. With scrabble, you learn more words to get better. With poker, you learn more plays to get better. Study more, and the money will come.
4) Um, the difference is huge, but the main idea is that in a ring game you're usually playing deep stacked (if you're playing no limit), where as in a tourney, you're short stacked relative to the blinds.
5) Consider playing sit & go's if you are short on time. Ultra Turbo 6-man sit & go's can take as little as 15 minutes. Plus, I think sit & go strategy is much easier to learn than the strategy for ring games, and its a great place for a beginner to start.