1. I think that this seriously depends on your child's learning style (I would recommend maybe having them take an online test to figure that out, it can help with lots of things). If they do learn from reading though, some of the people above gave some wonderful examples of books about Scratch. Personally, I just learned from myself, and I think most other Scratchers do as well, but I'm sure that reading a book couldn't hurt.
2. Well, technically a 2-year-old or a 122-year-old could both use Scratch and have a good experience, but if you want to know the average age of most Scratchers, you can view the Statistics
3. I wouldn't recommend homework, because I personally think that you should maybe introduce Scratch to the class, and first see how they like it, so, if they really enjoy Scratch and coding, then giving homework would probably be a good idea, but if they really dislike it, then I could see how coding could get very boring and not fun very quickly. It really depends on what the children think of Scratch, but I just really don't think that it would be a good idea to make kids not only code on Scratch during class but also give them homework.
4. Many people above listed some great resources already
5. No, but, if you find another teacher/ parent's account, you could comment on their profile asking for help with something.
Hopefully this helped!