I finally got Corsola to Level 40 so I have now finished getting every Pokemon in Johto completed to my goal! That makes 2 regions down and still quite a few to go. A pretty good milestone I’ve gotta say! The Pokemon remaining for the other regions are:

Hoenn: 14
Sinnoh: 22
Unova: 28
Kalos: 13
Aloha: 27
Galar: 7
Hisui: 3

So I might complete Hisui next but of course for that region as well as Galar they are still releasing Pokemon so that number may go up before it goes down!