Your comments about small elephants reminds me of "Stinz", the series by Donna Barr about "halfhorses". They also had problems with stairs, and angled ladders, while necessary on a farm, were a major pain. In fact, Ms. Barr went a lot into Halfhorse physiology, and the problems (as well as advantages) it created.

Also it's a good point with the distinguishing between agility and dexterity. Most games don't distinguish between the two characteristics, so you have weird things where the lighting-fast Kzinti in the Ringworld game are also incredible acrobats. I'm not sure that I want to go to the effort to do separate characteristics for Dexterity and Agility, but it might be something to think about.