Welcome to the im@s fandom

I second what liza said, the idolm@ster anime is a good start.
One thing to note there: Some characters are exaggerated compared to the games (Yukiho for example), and many get the short end of the stick in terms of screentime (basically everyone except for Haruka, Chihaya and Miki). In the games all characters get the same treatment when they are producable (so not for Hibiki, Takane and Miki in SP, not for Azusa, Iori, Ritsuko and one of the twins in im@s 2)
In terms of games i suggest the newest one: The Idolm@ster One For All, if you have a PS3. The game can be played without knowing Japanese, but understanding the visual novel parts adds a lot to it and especially the characters.