Appears Mike got some technical support ... the 'mentioned methods' above were communicated in a direct EMail to Mike ... issues resolved with exception of backing up one course. PHP time for script to run and memory to use increases were suggested - plus breaking apart the backup of the 'large course' into two backups.
So Mike is back to where he was prior to the attempted upgrade/hyperjump from 2.8 to 3.6/7. Now he can make backups, upgrade the site, restore backups to move forward.
Which brings me to this ... which is related ... (as been suggested before but ... ) on the Notifications screen where one sees the 'nag' about upgrading, an link to the Environment check.
All of this might have been avoided. :|
And ... the 'update component' link is perhaps the only link like that for admin level user ... seems to me that could be 'automated' as a scheduled task and the environment check files could be acquired prior to an un-aware/experienced admin jumping 'out of a pan' and 'into a fire', so to speak ...