Editing images in equirectangular format gets harder with the cosine of the latitude.

You could try something like this: Sketch out the map loosely in QGIS just showing the main features and layout, then produce templates from that for each region which you can fill in using Photoshop/GIMP, Wilbur or whatever raster tooling you like. Export as image at a consistent scale and DPI from QGIS making sure that the "worldfile" box is ticked; then you can edit the resulting file and import it back into QGIS, using the worldfile it originally generated, so you don't have to georeference it again.

You can get an orthographic projection centred on any point on the globe by using the Globe Builder plugin; navigate to where you want, select the option to project on the centre of the map, and select "Add globe to a map". Be sure to set the scale back to your standard. Alternatively make a set of your own projections by copying something like Orthographic North Polar and changing the lat and lon numbers in the Proj 4 script to suit.

Another thought is that if you use Mercator projection you lose the distortion as latitude increases in exchange for some unwanted scaling. So if you have a bunch of excerpts from a Mercator map, you can turn them into a common scale by resizing them by a factor of 1 / lambda. Gets fiddly at very high latitudes so at some point you go over to the orthographic polar.