Fist of all let me say this site and some of it's tutorials have helped me immensely.

I'm currently working on a world map for a book based off of a campaign my friend has run and a,m looking for feedback and hopefully tips.

A bit of background, currently I'm using photoshop CS6 for all editing since I like the layers and ability to try different things. The author had a previously drawn map on 8.5x11 that I am trying to convert into something a little more styled to his venue. Having said that I"ve got what I feel is a decent start on the land masses, rivers etc but I'm struggling now that I get to the artistic side.

Personally I'm somewhat comfortable with CS6, I'm a hobbyist photographer and have done some side jobs in basic graphic design. I'm much more comfortable with contrast and clone than I am with brushes and painting. Graphic design work has been limited to page layout and business card design. This means I should be able to understand the majority of the lingo just not the application of technique. I know enough to know I don't know enough.

Let's start with the source material. Here is the original map.
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There's a lot of country/border information crammed into a little space with what looks like some very unnatural boundaries. I started by making some natural boundaries to try and make it look a little more logical for a D&D campaign but there's still more work to do there. Any advice on that front would be appreciated.

After reading and working some with the general layout I've come up with the following general layout which we are both happy with.
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I've stretched things out and added some more water content to try and make it less of a ball of rock and more of a world.

From there I've got to start working on the mountain ranges, forests etc. I've got quite a few brushes that I'm happy with and thanks the layers I can get these on fairly easily but from there I run into some issues. Texture and general ageing should be fairly easy based on previous experience. Here's a quick example of the style. I'm looking for more antique or fantasy and less atlas for the end result.
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My main concerns are adding some color, realistic country borders, and possibly creating a map grid to give it a sense of scale.

Color:
I'd like to keep the colors muted or washed out to keep the worn feeling but I've not done much paint work in photoshop so any advice or direction to tutorials would be appreciated.

Borders:
As mentioned, there's a lot going on here and some of it is arbitrary from the authors standpoint but I'd like it to make more sense than solid lines dividing countries.

Grid:
Not sure if a grid makes sense but I"m looking for some way to give it a sense of scale. Would that be in the mountain range, forest scale if not the grid? I'm new to cartography in general and have done a lot of research on the mechanics (Lat/Long, Typography, general principles) but knowing how something works and making it work are 2 different things right now.

Thanks in advance for and all feedback, hopefully with your help I can share something wonderful when I'm done.
I will say I'm having enough fun with this project that I see quite a few more in my future when this one is complete.