I’ve got plex and multiple home servers/NAS’ already. All my non laptop machines run RAID on all their disks (even SSD’s). They all have not just one but multiple offsite backups.
Plex is close to being the solution to the music as it’s one of the few options with smart playlists, but it doesn’t yet allow syncing the entire music library to mobile in any usable way.
Nextcloud looks very promising. The Exchange integration options are not great, but the software itself looks really nice. Thanks for the headsup on that.