So... is that "river" going through the big mountain and ending at each coast? If so... well... thats probably not very likely(though not impossible!) in a real world geography sense unless this is an island and that's a straight instead of a river.

You mentioned somewhere something about a cave? Well... if you flip the elements(mountains and forests/shadows), then you have a light colored surface and you can then "draw" in the cave mouth fairly easily.

As for Waterfall, where is it located? a cliff or somewhere on a mountain? Show us where it will go and then perhaps we can make the suggestions. Likely you will need to do some "editing" of the existing mountains if that's where you want the waterfall to be in order to make it look good.

For me, the colors are just waaaaay to bright.