Union Filesystems/Setting up a pool

Let me start out by saying I'm very new to both Linux and OMV and very very new to command line Linux.
Here's what I have done so far. I wanted to test out OMV, I made a simple NAS out of an old store bought desktop. Installed OMV on a USB stick and had one HDD for storage. Set everything up pretty nicely through the guides on this forum, online, etc. I decided to dive in and add my other HDD that I had in my windows desktop that had about 400GB of media. From reading it seemed like maybe Rsync could handle transferring the data from my NTSF formatted HDD to the EXT4 I formatted in OMV. This wasnt working for me as Rsync wouldn't recognize the data on the NTSF drive. I somehow managed to move the all my media from the NTSF to the EXT4 drive in the command line through SSH. At that point though the data was not in my "Shared Folder" I had created and I was having trouble moving it within the EXT4 HDD itself (through the terminal or extplorer in OMV). My mistake I believe is i hastily created a AUF mount point with Union Filesystem with the NTFS HDD and EXT4 HDD that was already all set up in OMV. I then wiped the NTFS drive, reformatted to EXT4 and moved all the Media back onto it.

My problems
- I now cannot create a new mountpoint with Union Filesystem (it only recognizes the newly formatted drive and not my original)
-I cannot reformat/wipe the original drive
-i cannot delete the AUF mountpoint or the shared folder I created in it.
What I want
-My two drives to be in one pool and try to save my media that is on the one drive. (Would be fine if we cant save the media/data its just movies and tv shows)
-I have an external HDD that has a lot of media on it, what would be the easiest way to transfer that to my pool (after i actually make one). Just plug it in my windows machine and drag and drop through the network?
Thanks for any help in advance!!

I gave up trying to untangle the web I created. I googled to wipe my drive via SSH in the terminal. Then I installed a fresh OMV on the Hdd instead of the USB. Once OMV was up and running, installed the omv extras, backup plugin and then Gparted. Shrank the partition down to about 20Gb, and then formatted the remaining unallocated space to EXT4.
Back in OMV I kept getting this error when trying to save settings in the WebGUI:

exception 'OMVException' with message 'Failed to decode
content (filename=/var/lib/openmediavault/dirtymodules.json): ' in /usr/share/php/openmediavault/util.inc:284

Through the forums one of the mods posted this command which worked (I ran it in a scheduled task through the WebGUI as the mod suggested, since I couldn't enable SSH and didn't want to hook up a monitor)

echo "[]" > /var/lib/openmediavault/dirtymodules.json

After that was a success I then ran into a mount error when trying to mount my two Hdd (both formatted in EXT4), this was the error:

Failed to mount '5964e6c8-3655-4a7f-bdd3-fdb40fc5cb6b':
mount: can't find /media/5964e6c8-3655-4a7f-bdd3-fdb40fc5cb6b in /etc/fstab or
/etc/mtab

Found in the forums again another mod posted this command I ran through SSH that immediately worked and I was able to mount

omv-mkconf fstab

Once both drives were mounted I was able to create a Mergerfs mount point with Union Filesystem plugin.
Also figured out my troubles with Rsync, I was unaware when creating a shared folder you could select a path/folder already on the physical disk (the path/folder with the data you wish to transfer) Once I realized you could do that and, then easily Rsync that path(with the data) to a path on the shared mountpoint(pool) you created, it was a breeze.
The plex plugin was giving me an authenticate error when I tried to install, however that was fixed by a reboot.
Now I'm all set! We can mark this as resolved.
Thanks to all the mods and community for all the information on here!!