I think the friendliest will be sourcehut, which is both FOSS and works without JS too.

Here's a guide for gitlab and i2p https://geti2p.net/en/docs/applications/git-bundle

They’re self-hosted, as in 127.0.0.1 or 192.168.x.y

You can send any traffic through Tor, so yes.

For has a significant impact on latency, and use of JavaScript is often discouraged because it can be made to deanonymize users.