Seriously! What happened to Nullobject, it’s been months without an update.I have a Mistercade, like it, and I'm always happy to hear about alternatives or just comparing how things work, for what it's worth.
Honestly at this point no matter what you're doing with your mister you're basically an early adopter barely out of beta testing. Everything is raw and in flux, never know what's going to change or become a requirement as people figure shit out.
I'm happy with what I have. If I can't run Saturn games in my cab that's okay, though I probably would try the shmup ports at least. Right now I'd settle for the guy who was making the Cave core to stop being vanished, I keep paying into his patreon still in the hopes that he's still around in some way.
https://github.com/MiSTer-devel/Arcade-Cave_MiSTer
Patreon money collecting into a void