How do I script falling damage?

You can either define an "OnLanded" command/activity for the avatar, or you can just override the "OnLanded(..)" method in the Avatar class, and call your code from there. So right now, it *does* act as both a hard-coded override as well as an event called "OnLanded".

What do I do when my world projects fail to compile in Visual Studio?

Check to see if you have broken project or assembly (.dll) references, as this is a common cause of failed compilation.