Selfhosted

• Ever tested restoring those backups? Do you have the exact procedure written down? Does it still work? If the service gets compromised/data corrupted on sunday, and your backup runs, do you still have a non-compromised backup and how old is it?
• How timely can you deal with security fixes, and how will you be alerted that a security fix is available?
• How do you monitor your services for resource availability, errors in logs, security events?
• How much downtime is acceptable for routine maintenance, and for incidents?
• Do you have tooling to ensure you can redeploy the exact same configuration to another host?
• How do you test upgrades before pushing them to production?

Not saying this is impossible, you just need to have these questions in mind, and the answers written down before you start charging people for the service, and have the support infrastructure ready.

Or you can just provide the service for free, best-effort without guarantees.

I do both (free services for a few friends, paid by customers at $work, small team). Most of the time it's smooth riding but it needs preparation (and more than 1 guy to handle emergencies - vacations, bus factor and all that).

For the git service I can recommend gitea + gitea-actions (I run the runners in podman). Gitlab has more features but it can be overwhelming if you don't need them, and it requires more resources.