You're making it much harder than it needs to be because you're used to operating in 2024 mode. Roll back to 2004 mode.
You probably don't need to sync everything.
You probably don't need a backup vendor.
You probably don't need to change the OS.
You probably don't need a homelab or massive cluster to run all your stuff.
For me, all I've done is turn off iCloud sync for most of the stuff and deleted the data in the cloud. Backups are handled as before: on/off site rdiff-backup to physical disk. Email I moved to a local provider that runs IMAP and keep nearly all my folders offline. Code? You don't have to push it somewhere!