Archy

piped.video still works for me: subscriptions, categories, comments. Watching is MPV

Google it

For me paru, but never tried Aura

There is an interview with the founder on one of the Privacy podcasts. You can form your opinion. My opinion - yes, they are trustworthy and you can do with them anything that you can with any Linux box, alternatively flash a clean OpenWRT for extra paranoia

Signatures are different. Uninstall old FDroid version first

I’m not your buddy, bro

look on XDA developers forum for your model. They usually have plenty of alternative ROMs

It definitely has to be Jellyfin (server) + Finamp (client) + tailscale (mesh VPN)