My first PC was a 486 SX, 300MB hard drive, 24MB of RAM (a lot at the time), an impossibly heavy full tower case, and only MSDOS. I later borrowed a Windows 3.11 disk to install, but the knowledge I gained from playing around with DOS (mostly trying to get games to work) was invaluable. What about you?
Whoah, what a coincidence, the first PC that I bought was 486SX too

486DX was so expensive compare to SX ... probably like i5 vs i7 today. Regardless I was able to play DOOM 2. I was thinking: whoah it so realistic (sweat memories) ... Thats funny because few days ago I finished Doom2016 and you can play the Doom2 inside and I was thinking: How much graphics had improved over the years...
Squall, this is a mock-up of what I envision the UI to look like:
Hehe, I said you are very creative person and you didn't disappoint me

very clean, intuitive, stylish! I wish you work for us and make the design for new projects :D
Unfortunately, there are few problems that I have to address:
- as far as I understood, the game allows you to mix commands and notes. This design would allow only a 'header' with commands and then notes only. I'm not musician, but I guess you may want to change the volume, tempo,... during the song
- changing octaves would require to 'record' when they are changed. That is a source of numerous edit problems - when you shift is it after the last entered note or you have to add some sort of markers of where the change starts. Also when generating the hex, what commands should I use - relative (E1/E2) or absolute (DA)
- what you see on screen is very small fraction of the song. For real songs I guess that will be enormous scrolling left and right, which is very tiresome for the eye and concentration. Add to that octave change visualization ...