What a nightmare. Had to recompile and reconstruct databases and then recover tables from Time Machine. Multiple pages trying to figure out MySQL issue, including InnoDB reports that I had corrupted database. Frustrating was an understatement. I seemed to have three versions of MySQL running. Finally got things removed and proper things reinstalled and then, out of nowhere it started working again. Seems like some of the errors caused by leftover error files in the MySQL directory. Once they were deleted and restart, all was well. Homebrew wasn’t helping much. I had to back down PHP to 5.6 (7.2 may have been part of the problem.
I now seem to have all of the High Sierra transition issues resolved, including needing to restart in recovery to disable system integrity checking that was keeping an errant file in the trash with no way of purging it. Once that file was gone, system seemed to return to normal stability. Reinstated the integrity checking and all is well.
I enjoy Homebrew, but the troubleshooting can be painful at times.