Looking good so far Psylence, there are a lot of interesting things going on! I like the style of your map key, simple but effective.

I struggle with borders as well, but I know that arsheesh has a quick tutorial floating around here somewhere covering the basics...
http://www.cartographersguild.com/tu...ders-gimp.html

I think I agree with fabio p that it would be interesting to see this with a thinner neat line.