1. I've used that before in my code. I don't see why you couldn't use it(I have also seen it be used in other libraries)
2. It depends. If you need to interact with the DOM right away(as in, find elements, change properties, or set element events), the code has to be at the bottom of the body. If it's just function declarations and definitions, you can keep your code in the head
3. Is this a question?
4. There is nothing that really pops out. You have very nice spacing in your code(everything isn't bunched together) and your formatting is perfect(in my opinion).