You may already be working on some of these (or maybe they're in the game and I missed it) so I apologize if they're redundant!
- The dance/vocal staffers with no stars in coaching can't coach any girls at all since they cap at a stat of 1 (I've never rolled a girl with a 0). This can lock you out of coaching altogether unless you can afford another staffer, and even then they just sit there consuming resources uselessly due to the need for scandal points. This doesn't happen with the managers since even managers with a 0 in deals can still do business proposals, and 0 stars in production doesn't stop any staffer from producing. It just feels bad to have an "incomplete" staffer, so to speak, and makes the staffers that start with stars in coaching much more valuable.
- Loans can be hard to find. Some kind of shortcut to loans from the money indicator in the UI if your money's running low or is in the negative would be pretty useful, especially for new players who make bad choices of room purchases at the start (you pretty much need loans if you build every room except an office).
- I know you can see how much stamina (and weekly stamina) an idol has when choosing them for business proposals and shows (mostly through tooltips) but making it more easily visible (or at least a warning that it'll go negative if you accept/launch) would be helpful.
- Singles on physical media feel a bit underwhelming between having production costs and no knowledge of projected unit sales - it'd be nice to know how many units you're potentially going to sell, like projected ticket sales for concerts.
- TV Drama contracts are very very taxing on stamina (sometimes needing 60+ weekly), so they feel a little underwhelming compared to other proposals, even with the other benefits. Since girls need stamina for concerts and other gigs, I often find myself passing on drama contracts unless the stamina cost per week is low.
- It feels like girls' fame and production skills for staffers rise very slowly compared to coaching and business proposal skills, which can be maxed relatively quickly.
- The producer's influence rises extremely slowly right now, could never get it to above 2 and a half stars.
- Research is expensive (especially considering your staff can't be doing anything at all to get research points) and the related skills rise very slowly. With more money than I know what to do with, max coaching/business and production skills in the 80s, I barely have any genres at higher than rank 5 - the balance seems a little off.
- World Tours seem very accessible very early on, especially considering they're the final requirement for gain per performance. You'll have been able to go on several of those before reaching rank 10 on a specific genre (previous requirement).
- Getting ¥100,000 for a photoshoot job (promotion lv.5 requirement) is really easy. ¥100,000/w from advertisement (lv.4 requirement), however, seems to require several rank ups. Typically by the time I manage to hit that amount, +350 fans are negligible (they'll be in the hundreds of thousands or millions - I tend to focus on pumping out singles and concerts).
- As a whole Promotion seems objectively inferior to Performance except for very very early on, all things considered.
- Media seems to be the fastest way to increase fame with a fixed cast but I've never managed to turn a profit from it and it's super taxing on the girls' stamina.
- Active shows should probably be on top of the list at all times by default, they can get buried under canceled shows, I think?
- When you have a ton of idols it can be really difficult to find them in the list and/or tell them apart. More color variations in the assets would really help with telling them apart visually. It'd probably also help if auditions couldn't give you hairstyles you already have on your roster (unless repeats are unavoidable, but that's where varying colors would really come in handy) since the idol's face tends to be the main visual cue you get and the hair is the main thing that sets them apart (faces help, but much less).