It’s probably most important to make the complete switch to a “Free” OS (*Linux, *BSD, …) first. You could then run a small homeserver that fulfills everything you need. I think for this kind of homeuse Nextcloud is suboptimal because the fileops are done with WebDAV; server-based homedirs with NFS are much faster and more flexible. Another easy way to sync/backup everything on your home-PC(s) is to run regular (eg on startup/shutdown) syncs/backups to this homeserver on them. you’ll be amazed how fast and easy this is in a linux-environment.
disk-redundancy does not protect you from accidental (ie human error) data loss, but you could use a variety of fs-snapshots.
for the personal data on your phone nextcloud is just perfect (i cut ALL contacts to google et al in the days when nextcloud was still owncloud (9, i think)). It works best with a “real” internet-server but can be made to work with a dyndns-home-solution. the nextcloud-datadir (and everything else) must also be backed up, of course, which can be easily done from your linux homeserver (ssh pull etc.)
GOOD LUCK!