The rivers were mainly there to serve as a guide for those new folks who need to see how rivers look...in a rough sort of way. The mountains are going to be a hand-drawn style so I can plop them into the larger blank spaces. I never focus too stringently on how real the geology might be so yes, the mountains should come first in order to determine where the rivers are, I just thought I'd try the opposite approach and lay in some rivers to determine where the mountains would be. I just sort of let my hand wander around making squiggles and see what happens. I start with a few long rivers attached to inlets or bays, then add some branches to them, then follow up with smaller rivers to fill up space. Once I see a clear blank spot appearing I then start planning my branches to go towards that blank space. My biggest concern is that this is going to be too small and might have to go and double it...trying to force myself into doing something small though.