Another Atlas lover.. I can relate. To me it felt like I had a book full of treasure maps and adventure.. if that makes any sense.
There's a great Tutorial/How-to folder in the Mapping Resources section of the forum. I don't use it myself, but I believe there are some GIMP tutorials as well. Maybe get a Work In Progress post going, and if you get stuck just ask for help. I know there are some very talented folks here who use GIMP.
As for your writing.. this site does have a BLOG feature, so maybe post some of your stuff.
Welcome to the Cartographers' Guild!