Hi Leslie,
Reading your post, I think I’m running a similar setup (home user, intermediate Linux knowledge) and had similar questions.
I am running a NexctcloudPi instance for some years now: Started on RPI3, moved to RPI4 - both setups based on NextcloudPi_RPI-images. (Meanwhile i moved to Intel-Hardware using NextcloudPi “clean Debian installation” via CURL-Script).
My answers / based on my experience:
No. From my point of view - it’s nice to have. I never made it that far 
From my understanding, NCP scripts do support BTRFS out of the box for external USB-Drives “only”. Please have a look at https://help.nextcloud.com/t/how-to-configure-an-external-usb-drive-with-nextcloudpi/126376
However - if you are able / willing to deepdive into maintaining /etc/fstab manually (without NCP script support) you should be able to add your NVM / SSD drives (including BTRFS filesystem).
You’ve probably already done this anyway to get your “dual nvme slot / 1 western digital nvme 1TB ssd” up and running?
Best regards
schoetju