AFI released a list of the top 100 American, English movies in 1998, and updated it in 2007. It's a Wonderful Life is #11 on the original list and #20 on the update.
Academy Award for Best Picture refers to whatever the equivalent award was at the time.
No major spoilers, but the explanations do have further spoilage.
BTW: In your explanatory note for Q12, you missed the r in Wonderful.
Fixed.