Hello there, I had actually gotten started on writing my own version of this myself, but seeing as how you've beat me to it (with incredible quality I might add), I wanted to put some thoughts here in case it helped!
-The fact that you captured The Zone is amazing so great job. I think it would be neat if everyone player character was given a single, one time use, "A star is born" kind of moment, where they can manually enter the zone. "Whichever horse wins the derby is the luckiest" but that really sucks as a player to have you moment be crafted throughout the game and then lose it to bad dice. Each player would only be able to use this once throughout the entire campaign.
-A small throw together table for making NPC uma's would be awesome! Just something quick to glance at, crunch some numbers, and throw another couple racers in would be amazing.
-An encounter table/guide would be nice. I know it's super early in development, but I wanted to mention it! The events in Uma Musume can be, "varied" is how i'm going to put it, so perhaps two or three little suggestions per hobby selected would great.
-Perhaps a fun roleplay to involve the idea of trainers as a more distinct character: Players build their Uma Musume, and then a different player acts as the trainer for that players Uma Musume. This could maybe be an alternate ruling, but I think that would alot of really important burden off of the GM who is already having to balance alot of plates with this system.
It looks amazing so far and I can't wait to see where this goes! I'd love to contribute in any way I can if you would ever want the help of someone spare.
First of all, thank you so much for the kind words and I'm really sorry for the late response 🙇♂️
We designed the zone to essentially mimic critical successes from DnD, so the fact they occur randomly is intended. That said, manual zone sounds fun! Allowing it once per campaign might result in some players keeping their one time use until very late in the campaign though.
To be honest we didn't even think about an NPC or encounter tables! Can't think of any reason why it wouldn't work. We'll see if we can make it happen in the hopefully not so distant future.
Although there isn't a formal rule set that allows players to play as trainers (yet), you can absolutely still do it with the caveat that trainers only roleplay. Another good way to ease the burden off the GM would be to suggest to your players to be part of the same team. Or at least not have every player be in a separate team with different trainers.
I really appreciate your post and feedback! We aren't capable of expanding the team right now, but we'll 100% keep working on both UMA RPG and other projects.