This is very similar to the way I have ended up doing my maps - it's interesting to read your methods here. I'd be interested in more detail on your colouring process. I'm guessing a normal colour layer for each area with some overlay or soft light layers for the shading and detail?
Also - you mentioned in another thread going through old books for paper textures - do you always use a scanned background or are some of the backgrounds computer generated as well?
Thanks for sharing the tips!