Also the matured DAW Ardour (floss) is worth mentioning.
Renoise (non free) and MilkyTracker (floss), if we allow some trackers on this list.
I prefer a regular WM on a desktop and a tiling WM on my laptop. So if you dont have a good mice i would recommend a tiling WM. I personally use xfce and i3/sway. But i would suggest to try them for a while with a basic configuration, and if they serves you well, cofigure it to taste.
That really looks interesting. I have a similar idea for such an application in the back of my mind for some time now. This comes close to it. Another application thats worth mentioning is cherrytree.