I'm honestly kinda surprised this is possible on RPG Maker, mostly since I'm used to seeing Wolf RPG Editor being the one used for more flexible projects. I do remember there being a rhythm game script for Ace, but that doesn't seem like that's what's being used here. It's honestly impressive if you've done it yourself, at least based on your Patreon's description saying you've been working with RPGM for over 8 years.
I'm not really a fan of the BF system you're using, personally; it feels kind of counterintuitive for a rhythm game, especially as it seems like you're mainly supposed to just get to specific parts and then take intentional hits. I guess it's something you can take with a pinch of salt though, as the system probably won't be within its intended design until more difficult charts are added. What about the monster girls using some sort of charm effects, that would make the chart harder or "glitch" the song if you get hit by them? I feel like the song glitching would add to that effect, but I'm not sure if that's possible within RPG Maker's limits. The charts themselves feel like they could use a bit of work too, notably with the pause in Follow Me feeling kinda awkward. Seems like this isn't really necessary feedback though, based on your situation with the artists, that's pretty unfortunate.
I know a few repositories you could try looking through, just gotta look through their licenses, since I know at least one of them bans H-games from using it; do you have a Discord I could send you the links to, or would it be cool to post them here (that's partially a question to potential mods too, I'm not a hundred percent sure if randomly posting a bunch of links would be alright)?