If you real want to get this right, you need to deal with projections. Projections suitable for the full globe aren't much good for larger scale maps, and vis versa.

I'd suggest starting with a very rough global map. Just enough to have an idea of the extent and location of things. Then do regional maps in suitable projections. I'd favour Conformal projections for this: Normal Mercator for the rough global map, Lambert Conformal Conic for wide areas in mid latitudes, Transverse Mercator for tall areas, and Stereographic for the poles and maybe for compact areas.

Then you can put everything in a common global projection to combine it. Normal Equidistant Cylindrical would probably be a good choice for data you plan to reproject into other forms. For a final global map, there are a lot of choices. I favour Winkel Tripel myself, though it looks rather "modern" and might not be suitable for fantasy maps. A pair of hemispheres in equatorial azimuthal projections work well and have an interesting look about them. Normal Mercator is good for a map emphasizing marine navigation.