If you’re interested in a Docker setup, I wrote a guide on how to set it up in Ubuntu.
It will be functional, but bear in mind 1.) performance will match what you put it, 2.) some addons (e.g. Collabora) will not run on ARM.
Nextcloud requires a single mount point for its data folder. Beyond that, how you arrange your drives (RAID, etc.) is a lower level system function not visible to Nextcloud.
You can host another website virtual host on the same server, but consider carefully how much load you want to put on a $35 board.