What's a good entry point for The Idolm@ster? i know that The Idolm@ster started out as a raising sim/rhythm arcade game in Japan but there is also a bunch of Anime and Print Media of it.

Is there is a game/anime/manga which is in English in one form or another (either Dubbed or Subbed for anime or officially translated/localized or fan translated for everything else) which would be a good entry point into the series?
How about this youtube channele?
You can watch promotional videos and radio programs that you can watch for free; original, Million, Cinderella, Shiny and SideM are all treated.
Anime and specials are distributed depending on the time.
Since these are Youtube, most content has auto-generated subtitles;　
somewhat inaccurate, but automatic machine translation is possible.
(If you choose English or ’英語’.)

Of course, these are legal content operated by copyright holders.