This is a great looking map - looking forward to more! And using a mouse for this? Fantastic job; you must have plenty of patience ^.^ If you're looking for patterns/textures you should check out ,cgtextures, 2textured, and spiralgraphics for starters. Spiral Graphics in particular is great - they have a program that lets you generate textures and give you great control of those textures. You can, of course, just download pre-made textures, but it's nice to have more control over them ^.^ Try using masks too to mess with the textures' opacity levels without actually erasing the texture. & Don't forget to try the layer modes like overlay, screen, soft light, &c. - they can really make a difference.
Really liking this so far, and good luck with that campaign!