@kbullkar - welcome to MobileRead.
As you found in my quoted text, the idea of some kind of tag mapping tool has floated around for a while. I lost any personal motivation to write it because nowadays I just use the Goodreads plugin for my tags, and I ensured that it has a tag mapping mechanism inside it that does all I need. I know this doesn't help people out there who have existing tags, unless they are willing to erase them all and just grab from Goodreads, but as that is a possible workaround my care factor isn't sufficient to spend the time coding an alternative
. That doesn't not mean someone else could not do so of course, I am sure there would be users who would like it.
For series/title, have you looked into metadata plugboards? They should solve your issues with prefixing the title with the series when sending to your Kindle. You can get a report of books missing in a series out of the Quality Check plugin. However it can never tell when a series is missing "later" books, nor does it have any integration with websites like Goodreads.
As for authors, what I do is use the Quick Preferences plugin to juggle between my various regexes when importing. It doesn't however solve the "FN LN" vs "LN, FN" issue. Trying to come up with a universal name switching algorithm is problematic as Kovid/chaley have mentioned a few times, particularly when you consider calibre is used to store non-english named authors as well. Usually I have drilled down into that author with a search (in combination with Alt+A) before I add a book for that author. So it is easy enough to do a copy/paste from the "proper" author name of an existing entry over the top of the new book - either individually or via the bulk editor dialog. For when multiple authors, I agree it is a pain, and I personally end up manually retyping the whole series in LN1, FN1 & LN2, FN2 &... format. But it doesn't happen often enough for me to code up an alternative
Good luck should you choose to write something...