OpenMediaVault VS NextCloudPi

You might want to consider the previously mentioned MergerFS and SnapRAID, or MDADM and LVM for your setup. OpenMediaVault [https://www.openmediavault.org/ is a solid choice in this regard. Additionally, if you're planning to run something like Proxmox, you could look into deploying Starwind CVM on top of it. Pretty much like in this guide: https://www.starwindsoftware.com/resource-library/starwind-virtual-san-vsan-configuration-guide-for-proxmox-vsan-deployed-as-a-controller-virtual-machine-cvm/ .

You would better to install OMV instead. It's a ready to use fileserver solution with web interface.

So I'm working on a similar setup with an ancient desktop my in-laws were getting rid of. I installed OpenMediaVault directly to the hard drive (it's so old that I assume it wouldn't work too well as a hypervisor), with a 4TB external HDD attached. OMV supports Docker by means of a plug-in and I'm running a Jellyfin container with no issues at all. I'm still manually downloading everything to the HDD but *arr containers are my next step, as well as setting up a gluetun container to route all that through a VPN.

That is possible (it's automated to a certain extent). It also depends on the NAS OS. Unraid, for example, can work with drives of different sizes while using the largest one for parity. TrueNAS uses ZFS so you won't be able to just add a drive to your RAIDZ and expand it. There's also openmediavault: https://www.openmediavault.org/ that uses Linux Software RAID and you can add a new drive there but you can't combine drives of different sizes. And there's also Starwinds NAS that supports both Linux Software RAID and ZFS: https://www.starwindsoftware.com/san-and-nas. Plus, I would avoid SMR drives in RAID: https://nascompares.com/answer/list-of-wd-cmr-and-smr-hard-drives-hdd/

I'd put it like that: if you have a spare PC, then it's definitely worth trying. I would also look into openmediavault (minimal RAM needs): https://www.openmediavault.org/ and Starwinds NAS (supports both ZFS and Linux software RAID): https://www.starwindsoftware.com/san-and-nas

nextcloudpi.com

It works great and is reasonably fast if you connect it over ethernet. If you have a newer firmware, which has already enabled the boot from SSD on your pi it is super easy (otherwise just Google how to set up boot from ssd with a microSD). Afterwards you can use the raspberry pi flashing tool to flash the image of nextcloudpi on your ssd. This includes the 64bit raspberry pi OS, a running Nextcloud instance and some other handy tools (like help to set up security features). The first setup can be done with the IP adress of your Pi in an internet browser of a device in your network. Here is the link to the image of NextcloudPi https://github.com/nextcloud/nextcloudpi

Issue 2 still persists and after digging around found this issue reported on git https://github.com/nextcloud/nextcloudpi/issues/1752 but cant figure out how to sort it

Install nextcloudpi (https://github.com/nextcloud/nextcloudpi) Install Nextcloud app on your phone.

If you want to update faster than the docker image is published, you'll have to build the image locally: https://github.com/nextcloud/nextcloudpi

My best experience in out of the box comes from Nextcloudpi: https://nextcloudpi.com/

Nextcloud is functionally similar to Dropbox, Office 365 or Google Drive but is self-hosted so you are in control of your data. This version is a lightly-forked version of NextCloudPi, which was developed for SBCs like the Raspberry Pi. Only a few changes from upstream and some SysV initscripts were required to get this working nicely in Linux Deploy.