Oh that's really looking nice!!
Well, for borders, let me see what I did for my last map in this style..
Found it!! (clicky if you want to see the results)
I copied the base land layer, feathered inwards by about 3 pixels and deleted anything that wasn't the base layer (moving through all the overlying layers (kept the slope intect to the water). I then copied the base layer, set it to transparent, and added an inner shadow set to normal with a light tan colour at.. 2 pixels I think, that added beaches . I then brushed around with a spatter brush tipped eraser set to a low flow to take some of the beaches out.