A few notes about installing from clean:
1. Take your time. In first day, I would install OS, drivers and minimum essentials apps only.
2. For rest of week, slowly install the apps in order of...

64 bit drivers (.sys files) are installed to C:\Windows\System32\drivers.
Driver files for storage are in C:\Windows\System32\DriverStore\FileRepository.

Is there anything reported in the Event Logs?

Have you run a chkdsk on the disk to check for corruption. To permanently assign a drive letter, open Computer Management console (compmgmt.msc), then use Disk Management to assign a letter to it...

Check the presence and sizes of :
C:\pagefile.sys
C:\Windows\WinSxS
C:\Windows\Temp

What backup software are you using? The backup software may have deliberately not assigned a letter to prevent the backsups from being corrupted, damaged in any way while it is 'online' This is good...

Open Windows Settings, Settings, Notifications and enable notification, then enable 'Show notifications on the lock screen' and enable notifications for each of the apps you want to include.

There is another way and that is to use the Office Deployment Toolkit and use the configuration files with it to download the installation files. Then you can create an ISO from them.

e.g.
cd...

I tried Flight Simulator X and could not install it on Windows 10. It is just too old, even using Compatibility tab would not work.
If you have 32 bit Windows or an older version of Windows...

Instead of a sandbox, use Snapshots instead. So, before you do any install or testing, create a snapshot of the VM, then when you are done, you can revert the VM back to the Snapshot!.

See The...

Make sure that your primary Ethernet connection has a static IP address configured, instead of DHCP allocated. Also that it has a default gateway and DNS server configured.

As well as the deep freeze method, is to create a default mandatory user profile.
See Create mandatory user profiles (Windows 10)

Does the drive appear at all in Disk Management console or the Device Manager?

I believe this is a USB 2.0 drive. The cheap cable that came with it may not be good enough, try a more expensive USB cable to connect to your PC. Does the drive come with its own power unit or does...

You can find any policy setting using the GRoup Policy Settings Reference from Microsoft:
Download Group Policy Settings Reference for Windows and Windows Server from Official Microsoft Download...

Application notifications can be turned off via Settings, System, Notifications & actions. Locate the app in the list and switch it to Off.
Sometimes, apps can add update notices in Task Scheduler...