For 12 track projects, everything on the internal SSD should not be a problem. The bigger question is the size of your sound/sample libraries? Will they fit on the internal SSD that you select?
A full installation of LPX factory content on a 256GB internal SSD is probably ok, and certainly ok with a 500GB or larger SSD.
At the opposite end, a full installation of Native Instruments Komplete 13 Ultimate Collectors Edition is 790 GB. Of course, users can be selective about what is actually installed.
Edited
My M1 Mini has a 1TB internal SSD for OS, app, LPX factory content, some movie files, important files, etc. I never worry about space. My third party libraries - Komplete, HALion, and Falcon are on a 2TB ext hd. Working projects are saved to a separate drive.
At this time, I still using a 2017 intel MBP with 1TB internal drive with only LPX content (and movies, various files, etc.) and no external drives except to acces archived files. Everything on one Mac no problem.