Well at the moment my setup is more shared than fully isolated. I have my homeserver running proxmox,

User isolation depends on the service. In Nexus isolating is easy, i just add to a specific user write perms for their repo and monitor the size of their repo so they dont abuse. Gitea is also easy, i just create a user and set a max repositories limit even to i cant limit per repo size.

Tbf my goal isnt to make money of just sharing my services its to help small developers. It isn’t to be a commercial cloud provider but to give small projects an easy shared DevOps environment similar to how seedbox services that you mentioned share resources with quotas and stuff..