Projection concerned, I would advise you to work on a version in equiretangular projection, and a very large file. But only for the line work on landshapes and geographical markers (rivers, ridges, mountains), and keep those markers on separate layers.

Then, whenever you want to make an actual map - I mean, with coloring, labels, and so forth - you take that file and plug it on G.Projector. And there you choose your projection and output it into a new file. In fact, output a version with clean landshapes, one with clean landshapes plus a graticule and a third with all your markers.

Turn those three files onto a three-layers file. That is your actual starting point for a map... from there you can retrace and do all sorts of cartographical neat stuff!