I'm having issues with the foreshortening on this guy's arm, and something weird is going on with his legs. As for the composition, I was thinking of maybe having him stand on top of some cliff, but the canvas dimensions don't look that attractive. I'd appreciate any feedback!
Well it looks like you're drawing his left arm at an angle, but his right straight on (which is pretty unnatural given the pose of his hand). Thus we should see a lot less of his forearm and a mostly straight-on view of his upper arm.
You might also consider enlarging his left thigh as it's smaller than his right (and by human standards, his knees should touch his chest if brought to the body) and shortening his tail as it helps the composition flow better.
Composition-wise, the white space size I made this example is about how far I'd go out for a background. Go too far and you lose the focus. I'd also place any solid masses (the cliff, far-off cliffs, etc) below and to the left of him to support the flow of his position.
I don't think there's really much wrong with the legs/feet. I like the proportions on the feet/calves in particular. They look good. The stance is solid and the face is amusing. Keep going!