Hello,
We're a small but friendly forum.
Have you watched the 2011 anime? If not, then I suggest you do that since that's how a lot of us started. If yes, then I would recommend playing the games (which you've been doing). It seems you played One for All, so that's great. You can also watch youtube videos for Idolm@ster 2 if you don't feel like playing it on the PS3. You can also watch videos for Idolm@ster 1 as well.
Check out other Im@s stuff like the music albums, mangas, dramas, movie, OVA, etc if you feel like it. I'm sure you know about the wiki on this site, so keep on reading it. The people here have worked hard on it, so special thanks to them.