I suggest to skip the nextcloud. It’s a mess. Use immich for pictures and paperless for documents.
If hosting some other files that don’t fit those 2 categories, things like filebrowser or copyparty are great. Nextcloud is really quite the challenge tbh and imo not worth the hassle it is for a typical selfhoster… It’s hard to get the most out of it. It pays of for medium organisations maybe but not for just you and a few other people…
Look at dietpi. There is a regular pc version (x86).
Their own “we do it for you” software choice is somewhat limited, but everything is really easy imo. You can always install other things they don’t offer, with apt or docker or … But the basic dietpi system is a super reliable, super lightweight, easy to manage OS.
For the music: dietpi+jellyfin+ tailscale+finamp on phone. Tailscale on phone, point it to only use VPN for finamp. It works incredibly stable and reliable for me. I tried many other “make it work remotely” options first, tailscale is just magic. If it’s only for streaming music to your phone, I don’t consider tailscale a privacy issue at all.