It’s booted from a USB via kexec from stock, so it swaps out the kernel and I can then load whatever I like - only limitation right now being 32bit 😔

Tbd, still figuring that out

will all my Jellyfin traffic go through the VPS

Yes

and count as bandwidth used?

Yes, twice (download from home to the server, and upload from the server to the client)

I do the same thing - I have a 3TB limit, but usually only use 300GB, sharing Jellyfin to a dozen or so users.

Edit: I’m sure there are plenty of good VPS providers out there, I personally have been using NerdRack for a few years now (got a VPS on special and the rate is locked as long as I keep it). Looks like they’ll do $11/year right now for a KVM VPS that’s sufficient.