Your plan sounds good to me.

I am using gitea (which afaik forgejo is a fork of) for the same reason, also on an n100, and it uses very few resources.

I use Debian lxc and deployed gitea in docker using ansible, but using the lxc helper scripts should also work great

For backups I use restic (running in another lxc) to push the files and DB dump directly to an external server, not the entire lxc