1. Not a great GM either, so you guys have at it. 

2. Any year is preferable, but an do all first year if necessary. As a reminder, certain activities are off-limits for First Years. Things like Quidditch (Harry was lucky, damn lucky.) and Hogsmeade are off limits for First Years, and the latter is still off limits for Second Years. 

3. Either or. Getting into the root history of Hogwarts would be interesting, but unnecessary. 

4. A little out of column A and a little out of column B?