So if all is not perfect, all is well. Bottom line is that I have to relearn some mysql and phpmyadmin procedures.
I was able to rebuild my forum to a fresh install by importing select tables rather than the entire database, and it seems to have worked flawlessly. I only imported entries, userdata, and categories, which I assumed was the minimum required.
Also, these sql files were generated via the Backup page in my original forum, rather than mysqldump. So, I need to learn how to use mysqldump to dump select tables, or use Query in phpmyadmin to export/import select tables.
The root cause of my problems seems to be that at some point I messed up a table somewhere. Updating MLF fixed a lot, and now I know how to rebuild to a fresh install with the essential data, so all is well!
Thanks for all your help. Love this forum.