Thanks for the heads-up potential installation issues related to the live distribution USB approach.
As a fallback approach, would flashing the Jetson through a Windows host using Oracle VirtualBox (Ubuntu 18) running off an external SSD via a USB Hub represent its own set of challenges???
VMs can be made to work, but often need special setup. The external SSD, if formatted with a Linux filesystem type, e.g., ext4, would itself not be a problem.
The most common issue is that during a flash the Jetson will repeatedly disconnect and reconnect to the USB. Most default VMs will lose the USB at some point during the disconnects and reconnects. If you can guarantee USB always passes from host to VM guest without ever stopping access, then this should work. Every VM is different in how it sets up USB though, so it is up to the individual VM’s support to figure out how to keep the USB.