Usually it’s p2p, there’s a moment while initiating the connection where some server is needed for STUN/TURN (i.e. NAT traversal).
I assume some service may have a fallback for server broadcast instead of p2p, but none that I know of do such a thing.
That’s a good question. Kinoite does not version some directories, such as your home directory or /etc. Rebasing and then reverting the rebase will create some clutter. What I’d suggest is to use some utility to version your files, perform a backup before doing the rebase or snapshot your home directory using the builtin snapshot functionality of btrfs. Maybe something like restic would work for this case.