Brave sync server is open source and self host able.

Everything a browser syncs is syncable passwords, history, bookmarks, cards etc

The “issue” is there is not a user interface element to easily add the self hosted instance url

There are workarounds though

You can read my quick how to here

https://ippocratis.github.io/brave/

Headscale does not support funnels unfortunately

Tailscale is not completely foss.

https://tailscale.com/opensource

RPI4/400 is perfectly capable as a little home server. All it needs is a good SD card.

Owntracks,photoprism,monocker,brave go m-sync,libre photos,wallabag,radicals e,Baikal,Firefox sync,Joplin web,webdav server,jellyfin,vaultwarden,wireguard

Nextcloud is an overkill. Its just too much. I’d say better split down the needed services. Baikal/radicale etc for contacts/calendar. Photoprism/librephotos etc for photos. A webdav server for storage. And so on.