I found the issue - minimal rights in C:\scripts. I gave appropriate rights and everything ran fine. Not really sure why rights were so limited in the first place but glad it's now working.
When I get to the SQL 2016 installation step, using the script you provided (modifed for my environment, of course), I get an error in a pop-up dialog box: An unknown command-line option [/CONFIGURATIONFILE=C:\Scripts\ConfigurationFile.ini] was specified. I've tried several things but can't seem to get past this. Thoughts?