I've had some time this morning to dig into this again. Contacted Apple support once again and worked my way up the chain to a senior support person. I've now got this issue assigned to a specific person that will keep in touch with me over the next several days to make sure the issue is resolved.
The new step I was instructed to do this morning was to edit the permissions on the external hard drive which stores the photos library. Even though my user account was set to read and write, and the checkbox to "Ignore ownership on this volume" was checked, she had me add Administrators to have full read & write access to the hard drive, and then click on the gear icon below permissions to select "Apply to enclosed items..." That part can take a long time to complete if it's a large hard drive. However, after that completed, I restarted the computer and opened up Photos. It had a little delay in opening, but not long and it's now going through the curation process. I was told to let that keep running...if I do have to stop it (which I will for going to work tomorrow) it should start back up from where it left off. She said that this process shouldn't take more than 48 hours, and at that point, fingers crossed...I'll be back up to running normally.
I really hope the permissions thing did the trick! If anyone has further questions about that process let me know! I'll continue to update on how this pans out. :)