You can’t apologize for asking newbie questions - that’s to apologize for starting to learn something new. Which is good, not bad 
Welcome to Nextcloud.
I’m pretty new myself, and had to try different approaches before I got a setup that I like.
What I wound up doing was this:
- Create all data areas for all users as Samba shares.
This way, I can access the files directly over the network, and not have to use the Nextcloud sync client (which will sync everything from the server and not show files it can’t sync when the local disk becomes full) or connect through Nextcloud with WebDAV (which is extremely slow) - In Samba also create shares for fixed collaboration areas, like “Common” or “Everybody” or “Multimedia” or whatever fits your bill.
- Still in Samba assign permissions to files and directories in the shares with
force create modeandforce directory mode - In Nextcloud set the data area to be somewhere on the local disk (I use
/home/nextcloud) or a folder on the external disk, but away from the Samba shares, and create the users - Then install the External Storage app in Nextcloud and create an external storage folder named with the username in each users home folder, and also create external storage folders for the collaboration areas, and assign user access rights in accordance to the Samba share access rights
In effect now, users will see their own folder and all collaboration folders in their home area
This way you can access the same shares both through Nextcloud and through Samba.
In my setup User 1 sees these folders in the root of the Files app:
- User 1 (read/write)
- User 2 (read)
- Common (read/write)
If a user creates a folder in parallel to the folders you set up this way, then that folder will only be accessible from Nextcloud.
One problem: The new Photos app doesn’t get any of this (or much of anything else for that matter), so I recommend using the old Gallery app (although it’s slow with external folders, at least it works):