Thank you so much for the help on this thread. The moral of the story, pay attention to what the pre-requisites say! You really do need to revert to the stock 7.1.2 version of Android for UBports to work properly. Once I reverted to that version, the installer still showed errors, but I just ignored them and pressed the "Try again" and it worked (filing bug report as I type). Now I am excited to see all of the features of the OS!

Thanks again!