No one has pointed out a basic tenant of BIAB: You do not have to install anything if you run BIAB from the external drive. If running it from your System drive, then you must install the app (this automatically installs supporting files but nothing else). With Audiophile especially, it's not unusual to install and run BIAB from your System drive using only the Drums and Real Tracks folders on the external HDD, saving about 1.3TB that doesn't have to be copied over. Your Projects and other Work files reside on your internal drive and you hardly ever back up your Libraries HDD.

There's way too much we do not know.

Usually (always?) when something like 700 files are lost, a basic mistake was made. When you are lucky, the files were just misplaced and dillegent searching will find that directory and you can breathe a sigh of relief. If you actually stored them on a HDD (mechanical hard disk), then recovery software can do a pretty good job of getting your files back. If accidentally deleted on an SSD (solid state drive), files are gone as soon as TRIM (part of the OS) and Garbage Collection (part of the drive's firmware) have prepared the cells for new data (anywhere from 5 minutes to 72 hours) and then there is no recovery. The higher versions of BIAB still ship on an HDD last I checked but this may be changing.

What Backblaze covers nowadays depends and it can only work if the computer is on and the drives are connected and awake. They have plenty of documentation on that—read and make sure you are set up the way that you need to be.

The problem with Backblaze is not the backing up of your fies; it's the restoration. You must get into the documentation so that you're never surprised.

BIAB 2025 Audiophile Mac
24Core/60CoreGPU M2 MacStudioUltra/8TB/192GB Sequoia, M1 MBAir, 2012 MBP
Digital Performer11, LogicPro, Finale27/Dorico/Encore/SmartScorePro64/Notion6 /Overture5