Hi John - To start my reply, I'm chuckling because of the applications I have regarding photo processing:
1. Aurora HDR
2. Luminar
3. Raw Therapee
4. Gimp
5. Apple Photo
6. Adobe Elements 6 that I never did figure out very well
7. Lightroom 6 that I use to import photos for the start of my viewing process and some digital processing
8. Digital Photo Professional 4 that I also use to view photos to see where my focus point actually ended up
9. NIK free apps
10. Affinity Photo
11. Snapheal
Whew.... I didn't realize how many I've tried over time! My history of photography was first quite casual. I'd take photos and be extremely disappointed with the results. Film wasn't my friend because it was expensive to send in for developing. By the time I got the photos returned, I'd forgotten what I had done. Digital has been a blessing but even that start was rocky. I didn't realize that a file size made a difference. And so does how one stores these files! Some of my early keepers have been lost due to poor organization.
During my exploration of photo apps, I realized I didn't really care for those that take over the process. I don't really like HDR stuff but it probably has its place and that some of the free stuff is harder than I want especially because there isn't decent documentation for it without a lot of hunting the web. Sometimes the apps are more complicated than I can understand - Gimp being one of those. My main apps to use now are Lightroom 6 and Affinity Photo.
I learn best by being shown how to do something so videos are first in line for information (decent presentations), next is text geared to explanation and photos to show results and last is the manual that is included with whatever gear or application that I happen to decide to try.
I'll definitely check out the three sources you listed. I'm game to learn. I don't mind studying so long as I understand what I am studying! <lol> That's where having mentors available is a plus!
Thanks for replying!