There are other projects other than Forgejo implementing ForgeFed. Forgejo itself has some federation support but AFAIK not based on ForgeFed. But they have a community contrib project that does.
- https://codeberg.org/forgejo-contrib/federation
- https://codeberg.org/activitypub-rs/activityforge
- https://frogue.vit.am/~ololduck/Frogue
Gitlab has a community epic to add ActivityPub support, but that needs contributors:
Generally you don't have to do this! There's lots of people running relays that are open access. But if you want your own it's very cheap. List of relays: https://tangled.org/firehose.club/community-firehose-list
Can you also fit a PDS to host yourself on on that VPS? Yeah I expect that it would fit very easily. PDS's have a lot less traffic hitting them than ActivityPub, they can be way smaller. They are quite lightly loaded! Because... there are relays in front of them!