2) Documentation: Code examples, easy things like: "This is what you send, this is what you get." "If you change this, now you get this." Simple example heavy documentation. 1 example is worth a hundred lines of documentation.

This is the only point that I care about (and 5) for being relevant). SO MANY TIMES I have tried to use an API only to find books of documentation without any working examples. Speak to me in the language your API understands, working examples, and everyone will have a good time. :-]