I tried to do this with a PbP game here called Legends of the North, but as I was working with IRL friends that weren't regulars on the board it became quite a chore to always be poking people to check the board. I'd totes do it again or help, but it does require lots pre-game work...
One of the most fun games I was in as a player was a solo game with an ST and a separate party playing other entities from time to time (such as an infernal coadjutor). Sadly the ST got mobbed by RL, but I will say that I've found it hard to play an infernal since that.
I want to experiment...
For map making I like to just skim google maps for areas that I can blow up and use. That way they seems realistic and yet not familiar. Generally g-maps -> gimp where outlines get pulled out and then layers colored/shaded as desired.
World Map
Close up of some islands (ignoring the pencil...