Kaleb - This is a problem with BackBlaze - their West Coast Data center in particular. I live on the east coast and was getting these timeouts on a regular basis. I resolved it by moving the backups to the East Coast BB DC ( and at the same time set the bucket up for immutable Object Lock for those companies that might need it some day.)
As for Forever Forward Incremental (FFI) , I DO NOT recommend using that for regular data file backups (documents, pdf's etc), only for VHDX or Image Backups.
The problem with FFI is that once you reach the number of days of the retention period, it has to do a Synthetic backup EVERY DAY. For example you do your first true Full upload on day one with a retention period of 30 days. On the 31st day the system does a Synthetic backup that rolls the day 1 incremental into the Full, (using something called "in-cloud copy") which takes a lot of time. The next day it does the same thing to fold in the day 2 incremental to the Full and so on in perpetuity. With 5TB of data, it takes a long time to do the synthetic folding of the incremental into the full. And with BackBlaze West Coast it all too often times out.

Now contrast that to regular file backups. You do an initial upload of all the files. Each day you run an incremental backup which uploads any new files created that day plus any new versions of a file such as a spreadsheet or QuickBooks file. You never have to do another true full, synthetic or otherwise. At the end of the retention period any old versions of files are purged from the cloud, but any files that have not changed stay forever.
For Images and VHDx backups it is a different story. Before the New Backup Format (NBF) we could only do a full backup once a month due to bandwidth considerations, and it took 2- 3 days for each one to finish. With the NBF, which supports Synthetic Fulls, we now can do a weekly Full and nightly incrementals. The synthetic fulls run on the weekends and typically take 80% less time than a real full backup would. We do not use FFI as it would cause the same issue as the file based FFI, each night it would have to do the synthetic Full folding of the oldest incremental, and could take too long.
So my recommendation would be to
1. setup a different email account with BackBlaze, and assign it to the Data Center closest to where your devices are.
2. Setup a bucket that supports Object lock immutability - (you don't need to use it in your backup plans but could at some point in the future)
3. Upload the 5TB of files - understand that it could take a week (or more).
4. Once the initial backup is complete, schedule weekly fulls and daily incrementals - understand that the weekly full will only do a backup of any file that has had changes during the week, such as a QB or Excel file. It takes only slightly longer than an incremental.
For any Image or HyperV VHDx backups (yes you can do that with the Server version by just uploading the VHDx files, set the retention period to one day. You will then have anywhere from one to 7 backups available for recovery.

I don't know your exact situation, but would be happy to assist you in designing the optimum backup plans.

Wow! I didn't know how good of an answer I would get but this exceeded all expectations. Thanks for the time it took to explain that!

I am creating a new BackBlaze account now while using my nearest data center and I'll let you know if I have any more qeustions

When you suggest weekly full, do you mean the option that says "execute full backup (synthetic full if possible)?

I use that for my onsite backups using a "file system" storage account. It seems to do a full backup and copy all data from what I can see

You are still using the New Backup format whcih you probably should not be using. DM'ing you some questions and more info.

@Steve Putnam
I found this post about the problem with Forever Forward Incremental and i can say that even with images backup, when it begins to merge the old incremental with the full it does a synthetic backup everyday that tooks insane hours to finish if we have a 1tb backup size.

I was taken by surprise by this behavior and if so, Forever forward incremental is not a solution to consider. It almost like making a 1tb full backup everyday. Insane!!

Don't use FFI for anything. But using the new backup format with weekly synthetic fulls (weekend) and daily incrementals works well for us. The weekday incrementals take only a very short time.