I'd like to get a smaller ARM based device and go client/server I'd like to be more client-server these days too, using whatever device is convenient at the ti

I'd like to get a smaller ARM based device and go client/server I'd like to be more client-server these days too, using whatever device is convenient at the time but storing my data centrally so all my devices can access it, it's all systematically secured and backed up, I can also access it remotely via VPN, etc. The key thing, though, is that I want it to be my server, not someone else's that I don't control and have to keep paying for.