I’ve tried to build a similar thing several times over the years - once in flash and once in JS.

Timing is the hardest - especially if you’re going to try to let people record on the fly against the running track. Have two or more play at the same time… rough.

And I suggest you checkout https://www2022.thewebconf.org/PaperFiles/40.pdf there is an implementation called wam out there that lets you use VSTs in JS. It works pretty well.

Good luck! I’ll be one of the first to sign up.