OK, so here is what I seem to have found:
1) after deleting my prefs file, but still working in my original user account, I have less frequent freezes, but they still do occur, and still have long "loading" times.
2) after setting up a new user account, opening LR, and importing 30 or so images, I seem to be freeze-free.
So now the question is, what next? If I reimport all my images from their drives, can I restore my adjustments, keywords, file organization, etc. from the corrupted LR catalog? And, if this problem is solved, I should be able to let the catalog grow to many thousands of images? These are large files, ~190mb. Is there a limit to catalog size without slowdown?
Again, your help is greatly appreciated.