Thankfully @kangalow saved the day without even knowing it. Just had to run the mammoth apt install from bootFromExternalStorage/install_jetson_default_packages.sh (github.com). At least it got me to the point that I could run everything. Doubtless would’ve fixed it from the start. Need to remember this next time.
Still some issues (e.g., failing a few of the tests) that I’m sure I’ll ask about in a separate thread. Regardless, thanks for all of your help @dusty_nv!!