Any solutions for PSE2018 time wasters ??

PSE5 was issued in October 2006. It's a dynosaur.

danielo97305100  wrote 1) When I select a photo to edit, it no longer automatically comes up in the Editor. When I close a photo after editing, it no longer automatically returns to the Organizer.

There is no reason to return to the organizer after a single file is closed. Most users frequently edit many opened files before going back to the organizer (a single click on the organizer icon on the bottom and you are back where you came from). If you close the editor (not a good idea), you are back in the organizer.

2) When I collapse a version set using the little arrow, it automatically expands the following version set for some reason.

True, that's a common complaint. I suspect the reason is that this feature may be 'as designed' to enable editing of a batch of adjacent files in some workflows. I don't like it and simply use the 'right click, version set, collapse' solution.

3) When I do a File - Save As on a photo that is already a version-1, PSE5 used to consistently suggest version-2. PSE2018 suggests version-2 about half the time and version-1 the other half. (It seems to get version-3 on up correct every time).

There is no change for me relative to PSE5.

4) You used to be able to check more than one keyword tag and bring up multiple groups of photos. Now you seem to be limited to just one tag at a time.

No, you still have the same features as before, and the wonderful text search to combine logically many keywords... and even substrings in captions!

Are there any legitimate reasons for these changes?

Legitimate?

Is this the kind of stuff that Adobe will fix in future versions?

Once you are used to a given feature, you don't like it to be changed, don't you? That means that if Adobe steps back to the older behaviour recent users won't like it either, so it's very rare that Adobe will 'fix' as you want. I'd like your second item (collapsing version sets) to be fixed personnally.