Beat the Idol Extreme with Chihaya after 40 hours of playtime so I'm marking this as complete (even though I still need to beat it with the other 12 idols but that'll all follow quickly).

It feels like it should be a lot bigger of a deal that this game has been fully fan translated, it's surreal to play a whole PS3 game this way almost feeling like it's an official localization.

The gameplay can basically be summarized as a sort of rhythm battle RPG, you level up your idols to raise their stats and can spend points in a skill tree. Each in-game week you pick a job, and 90% of the jobs you're going to be doing are the rhythm game. There's slightly different forms of it, with auditions, lives, festivals, and rank up festivals. Auditions are free so they earn you money, lives cost money but they earn you more fans, festivals are free but you directly play against an AI opponent. The AI can be challenging because they can do all the same moves you can do and use unique skills that can really mess you up. It's very repetitive but also somehow addicting, and it helps you can switch the songs you use as often as you want, along with a massive amount of songs if you install all the DLC (if you know where to search).

The other type of job available to you is promotions: there's only ever 2 available for each idol, a free one and a paid one. Ranking up replaces them with new promotions fitting for the idol's popularity level, but they're all short and not that interesting as commus so you don't really need to do them outside of grinding for memory points (more on this later) or skipping through weeks when you don't want to do the rhythm game. However make sure to do each paid promotion for every idol once they reach A rank because those reward you with accessories you can permanently miss if your idols later reach S rank. As far as I can tell you're not going to be penalized if you don't do promotions early on and end up having to do more of them in the late game, you'll still end up doing the same amount of them you would've done anyway to get memory points.

You start off picking one idol and the game pretty quickly gives you 2 more, after that you unlock a new idol after every in-game season (12 weeks) until after the 8th idol, the last 5 are unlocked every 2 seasons (apparently there's only 48 weeks in a year here). I only unlocked the last idol after 38 hours of playtime (I chose Iori last, also FYI it took me 33 hours to beat Final Fantasy VII). It's actually very easy to keep most of them within range of your highest level/ranked idol, they all earn EXP and fans even when you're not using them. I found I could just focus on doing jobs for my favorites (Chihaya, Takane, Azusa) until the other idols reached enough fans to let me skip rank up festivals for them, and use my strongest idols to carry the weaker ones through those. There's actually no downside to skipping rank up festivals, you can skip up to 3 at a time (for example, you can skip from C3 or C2 to B3 but can't skip to B2 or B1 without being B3 first) and you'll earn all the skill points in bulk.

Commus are different from the previous games, each week you can check if new commus are available, and doing them doesn't use up time, so they're completely optional and you could skip straight to jobs if you want (don't do this though). They've also been simplified, you either only ever make one choice that determines if you get perfect/normal/bad, or the commu doesn't have any choice at all and you automatically get a perfect commu. You're not penalized for getting bad commus as in you won't lose memory points, but the way the UI flashes the heart at the end of commus regardless of perfect/normal/bad still makes me unable to tell if you gain points or not from the bad commus. Some bad commus can be funny so you can just relax and choose whatever you want (but if you want to refer to a guide for perfect commus then https://idolmasterofa.fandom.com has most of them) and you can always get a chance to replay them randomly but you won't get memory points after the first time. To explain memory points, it's a heart that fills up extremely slowly, each time it becomes full it permanently increases the number of memory appeals you can use during lives, the max an idol can reach is 5. The game can also randomly give you commus before and after jobs, giving you a lot of chances to earn memory points. A lot of commus have 2 or 3 idols interacting with each other as well and will give you memory points for all of them.

Lessons don't use up time now either, you can do one before you choose a job. There's 3 types of lessons available and they give a temporary boost to one of the 3 stats for all your idols for 6 weeks. I appreciate this a lot because I actually still hate these minigames and I never used the lessons besides one time so far in this playthrough, so it's nice that they're completely optional.

This game has a significant time investment if you actually want to complete even one of the idol's routes, I can't recommend it unless you already love most of the characters. I beat the Idol Extreme with my first idol, Chihaya, after 40 hours. Getting story progression for each idol as she becomes more famous and unlocking new commus kept me going this long. Even after that there's all the DLC stories as well.

There's no fail state or week limit in the game, the most you can be penalized for is not achieving a season goal that Takagi gives you (such as earning X amount of money or passing X auditions), in which case you temporarily lose an idol, but you'd have to be explicitly trying to fail those since they're so easy. It's not a big deal to lose at a performance (though you can just restart the game before it autosaves). So overall you can play it pretty laidback and don't have to stress about doing anything too quickly (but you'll have to take festivals seriously as they can get challenging).

If you install all the DLC be mindful about installing the money DLC as well if it's your preference to play without being given a ton of free money on your savefile, because every time you load your savefile it'll nag you about 24 times if you want to use the money. I just went ahead and used them all however so I haven't actually had to worry about money management at all throughout this playthrough, I just want to buy all the outfits and accessories whenever they first become available.

Full disclosure I chose to unlock the idols in this order: Chihaya -> Takane -> Azusa -> Miki -> Yukiho -> Haruka (at this point I was feeling bad about keeping her and Chihaya apart this long) -> Ritsuko -> Yayoi -> Makoto -> Hibiki -> Ami -> Mami -> Iori.
That doesn't fully indicate my favorites though because I probably should've chose Yayoi and Makoto before Yukiho and it's more Yukiho's 1st Vision seiyuu I like instead of her current 2nd Vision seiyuu in this game.

Lastly there's a quirk about emulating the game in RPCS3, resolution scaling past 720p won't work because of whatever post-processing the game does and it'll just make everything more jagged instead, so if you wanted to see your idols in 4K it's not happening.