Some kind of scale would be nice, maybe, to make it easier to think about whether this all makes sense. Also this is a screen-breakingly large image. (oO_Oo)

It looks pretty cool, although I'm having difficulty trying to figure out the tectonic situation here. Is the dark brown the highest mountain ridge on the map, and the brown and grey respectively lower elevation contours, or do brown and grey indicate different heights of mountain ridges, or what? I like the inland sea as well, been playing with that idea myself lately..

As to labels: maybe import it into GIMP (or Illustrator if you have it) once you're done with the art and add the labels there?