No discord, never used it. But I recommend checking out my sequel Game Boy Hero II which does a much better job as it actually uses rhythm, unlike this game which just randomly drops notes. This was what I created the first time I ever opened GB Studio, so I still had a lot to learn, and I still can learn a lot more.
As for how to do it, there are two ways. I think the more common approach is to shoot projectiles and "catch" them by moving the player to the location of the button you press. My method is different, I move actors down the screen and if you press a button when the actor is in a certain position it records a hit, if they're elsewhere its a miss, or if they reach the bottom of the screen its a miss. As for when to start moving the actors, this can be done by calling routines (6xx) in the uge file for the music. There are 4 available routines, so it works great if you only use 4 buttons, although you could certainly create more complex code that can do more than 4, but then you have to worry about lag. Getting this to play on the DMG is a real balancing act of how much you can do before the lag slows down the game. You really can't have any lag as it ruins the rhythm, so you got to make compromises. Beyond that, its all just figuring out how the timing works which involved me creating spreadsheets and doing a ton of math.
By the way, I'm hoping in a month or two to have a big update for Game Boy Hero II with more than double the number of songs and an actual tour mode where you can develop a character just like in Guitar Hero and Rock Band games.