Tag/Keyword Import from Classic to CC (yes, again!)

I have read many posts on this subject but most of them are in reference to syncing between Classic, CC, and mobile and I do not need to sync (other than between CC and the cloud).  The keyword situation in CC is very frustrating having used Classic before where it was simple and intuitive; I understand this was a strategic decision by Adobe and that CC will never have the keyword setup that Classic had.  What I need to understand is this: can I tag all of my photos in Classic (using flat rather than nested tags) and then migrate everything to CC?  Will all of the flat tags for a specific photo migrate or only the first one?  I also understand that migration is a one-time only event and cannot be repeated.  (I am only using CC now and would have to purchase Classic in order to take advantage of its tagging capabilites.)  If I import each Windows file folder full of photos into Classic as a separate catalog can I migrate each one independently into a single/combined catalog in CC?  In other words, do I have to import all of my Windows file folders into one Classic catalog, tag them all, and THEN migrate to CC?  Or, can I import each Windows file folder into Classic as an independent catalog, tag one catalog, migrate that catalog to CC and then repeat with each catalog?  And, if I do the latter, can I migrate the second catalog I do from Classic into the first catalog in CC so that I can search across all photos?  (FWIW, if flat tags really do migrate from Classic to CC then this would be a one-time process for me with all of my existing photos.  All new photos would go directly into CC.)  Thank you so much!