I think the goals and themes of the two works are fairly different. Idolm@ster covered the 765 girls as a whole and tried to highlight them more as a group rather than individual sections. In CG, there's a much bigger focus on the trio and the other girls are supplementary to the core trio. I'm starting to suspect that the other girls, such as Oreki loli, won't get that much characterization and instead the show will heavily lean with the main characters for everything. I feel like it's a sort of stop gap measure in that CG really doesn't want all the side characters but due to Idolm@ster fans howling up a shitstorm if their favorite girls aren't animated, commercialization wins. It's a better approach than trying to deal with such an ungodly sized cast such as in the first Idolm@ster but the limitations of the work are also more apparent.
Thematically CG is also more about fairy tales. One of the girls had an orange suit on this episode that reminded me of a pumpkin and had also tapped her heels together like in Cinderella. There's also other stuff like the castle and whatnot. In fairy tales all your dreams come true and so I think the girls are going to do fairly well until the clock strikes midnight. They might throw in family drama though like in the original Cinderella. It's not a show focused on the girls slowly rising to fame but it all being more like a dream as they skyrocket to the top(which should present its own problems such as jealousy and infighting).
