At that capacity, SSDs won't be significantly more expensive than HDDs. I would get an external SSD plus an HDD for backups. For backups, any drive should be fine. You could also make another backup to Backblaze B2 withh rclone.

That actually looks cool. Are you looking to make sort of an article or blog post and publish the results?

There shouldn't be any issue with running Kubernetes in a Linux VM on Virtualbox. At least as far as I can tell. You can just try it.

NAS drives come with a longer warranty and are a bit optimized for 24/7 operation. As to and SSD, if you need uptime, then RAID. SSD can fail just as an HDD. Also, keep in mind that RAID is not a backup. Also, with backups, ideally, follow the 3-2-1 rule: https://www.backblaze.com/blog/the-3-2-1-backup-strategy/

I'm using an old Synology for backups. But for a NAS, you could build a DIY machine and put TrueNAS on it.

There will be no performance gain even if you passthrough NVMe drives to that TrueNAS VM as you still need connect storage back to Hyper-V (iSCSI or SMB). You'll just add more latency.

If you have an old PC, that could very well be a start. Otherwise, Dell Optiplex or Intel NUCs will be more powerful than Pi at the same price. Throw Proxmox on it and you have yourself a homeserver.

I would go with Ubuntu Server. Anys OS will need maintenance. Alternatively, Proxmox if you're into VMs.

And that is awesome!

Very cool and neat setup. Nicely done!

Damn you're lucky, that an awesome catch!

For data protection, you must first keep proper backups. RAID is for uptime, and for a homelab it's not always needed. Backups first (external drive, cloud), then RAID.