If you only need a bare minimum, and don’t plan to heavily use CI/CD, container/packages registries, integrations with other tools i would go with gitea/forgejo (you can always use external tools on top), else i would use selfhosted Gitlab, it has pretty much all the things you could imagine to need with software development and deployment

you can play on multiplayer just fine, as long as server have enabled offline-mode

For minecraft you can just use a offline mode in pretty much every 3rd party launcher, like SKLauncher