I`m not a pro, but:
1. You need to know C++.
2. I don`t know too. =
3. In short - Game is packed source code.
4. file size will get biggr if you add new code, so it`s not to much needed on your disc space.
5. I don`t know too. =
If i hadn`t said anything truly, of course all can correct me )