alwayssitting

There is a flatpak but it’s not published to flathub https://github.com/SoftFever/OrcaSlicer/tree/main/flatpak

If OP can find a V3 KE for a decent price then you get filament runout sensor and network connectivity, among with some other nice stuff. And for the failed print detection you can add a Nebula camera which isn’t too expensive if you order it from Aliexpress. It also supports rooting so you can add some really nice stuff to it, like Mainsail. I have a KE and I’m pretty happy with it since I got it for a really good price. I don’t think I would recommend it at full retail price though.

Try running a flow rate calibration in Orca slicer and adjust settings accordingly

Always had trouble with Nextcloud but ever since deploying it on NixOS it’s been rock solid. Both performance and reliability.

Try changing to another upstream DNS server in Adguard (such as https://dns.cloudflare.com/dns-query) and see if the problem gets resolved?

It will yeah, although with modern SSDs it really isn’t a big problem. I’ve used an Samsung 840 EVO as L2ARC for 8 years now.

Personally I would go for ZFS with the SSD as a L2ARC. But among the options you listed I would do BTRFS RAID1 if you’re only gonna use two HDDs, and mdadm RAID5 with BTRFS on top if using three.