So for better or for worse, I've 'finished' the example map from Mr. Curry's podcasts (up to #12). There are a bunch of things I'd probably try different, but just in learning masks, layers and some of the techniques, this was really a learning experience.

Thanks to RobA for the GIMP help. Much rep to you!

Now on to catch up to Mr. Curry's next podcasts and start putting his techniques to practice on my first game map - the Isle of the Lost Grave... o.O