> Knowing what I know now, if I started this project today, I wouldn't use Unity.
Have you thought about what you might use instead?
For those who don't know, back in the early 2000s, Nintendo and Namco developed a series of music rhythm games for the GameCube featuring Donkey Kong called Donkey Konga: https://www.mariowiki.com/Donkey_Konga_(series)
The Donkey Konga games borrowed heavily from Taiko no Tatsujin (another music rhythm game by Namco). However, instead of taiko drums, the player would use DK Bongos to jam along with music from different eras and genres.
Long story short, I figured out how to add custom tracks to some of the Donkey Konga games (Donkey Konga 2 and 3) but found the entire process cumbersome, so I decided to make a dedicated editor. It was a lot of fun to make, and I hope others get some enjoyment out of it too!
I quite like working with C#, but Unity introduces a lot of unnecessary overhead and isn't designed to build an application like this. I had to use goofy hacks to make Konga Beat behave approximately like a regular native application.