1) Yes you can do well at 1/2. Not enough to live on, but with bonuses and 4-tabling, you can make $15-20 an hour maybe more depending on your winrate. I think this is more true at 2/4 and even 3/6 and a lot of pros and semipros play these games.

2) Yes 3/6 is much much tougher. Just less bad players. That's all it comes down to. If you're playing against all decent players, it is hard to beat the rake at these low limit games.

3) You have to be tight. But if everyone is playing loose, you need to get involved with hands that play well in multiway pots, like small pairs and suited connectors. Read SSHE for good discussion of this.

4) There are pros playing at all levels online, more prevelant at 2/4 and above, the higher you move up the more better players pretty much.

5) Play on Partypoker and get Pockertracker

Good luck.