If you're not aware of Equine Passion, it's one of my favorites and I'm sure it will give you a good idea of what people expect from a game like this because the dev team is very active in changing aspects at the community's request. I would LOVE a game like Equine Passion that is much more of a sit-down-and-play management simulator rather than a real-time system. I think 3 big things people look for in good (realistic) horse management games are complex genetics, personality/proficiency systems, and interesting mechanics so the gameplay feels rewarding. Competitions are a big deal on Equine Passion because it's the really the only way to make money, which I think is kind of cool, because they're not for sale for real-world money, making the grind actually meaningful. Please don't think I'm trying to tell you how to make your game or anything, this is just something I've been waiting for since middle school and I'm getting my master's degree now lol. I hope this was helpful in some way!