I played SNGs for about 9 months. You can win $ and you can learn to beat the next level and all that, but honestly, I don't think 1k/month at the $20 SNGs is realistic. A fantastic ROI in SNGs is 25%. So if you're crushing $20 games, you'll be making $5/game. You plan on playing 200 games/month?
It's much more realistic to make this income in cash games, that's why I switched.
If you decide to go the SNG route, become a regular on the SNG forum on this site, it's superb.