Import all my photos to Organizer

This depends on your needs.  But I have been using the Organizer for about 20 years and have imported all of my digital images into my catalog.  I currently have over 200k files in my catalog, and I can only think of upsides to importing photos into the Organizer.  20GB of files should not take very long to import.  (My photos take up about 1.5 TB.)  I can find any file I am looking for within a few seconds.

I suppose the only downside would be the additional time to backup the catalog files using the Organizer's backup utility. 

So, I would encourage you to catalog all of your photos, even if you only intend to edit a small number of them.

I have ~20 GB of photos on my hard drive. Is there a downside to importing all of them? How long will this take? or do I limit the importing for just the images I would like to edit?