New to KDE - where should I start ?

I'd like to try KDE as a daily driver. I use Debian and Ubuntu. I am used to Mate and GNOME. I plan to setup a system with Debian Testing and see how it goes. I also have a Pinebook with KDE Plasma (I think with Ubuntu 18.04 LTS and an older kernel).

Where should I start ? Are there any recommended high-level user guides ?

What are the main differences between Ubuntu and Debian versions ? What do you appreciate the most in KDE that others don't have (other than widgets!) ?