I love tinc, it's so simple. I wish there were something just as easy that leveraged wireguard instead of whatever custom VPN/tunneling stuff tinc uses, as using it scares me with how seemingly little maintenance tinc gets. Like if tailscale/headscale and tinc had a baby, haha.
Is there a way to run tinc on your phone or similar? To me that's another bonus of tailscale at least.
I believe the Pictrs is a hard dependency and Lemmy just won't work without it, and there is no way to disable the caching. You can move all of the actual images to object storage as of v0.4.0 of Pictrs if that helps.
Other fediverse servers like Mastodon actually (can be configured to) proxy all remote media (for both privacy and caching reasons), so I imagine Lemmy will move that way and probably depend even more on Pictrs.