Danny Dot wrote:
If I buy an older plane that qualifies for Sport Aviation (e.g. less than
1300 lbs), but was certified "Utility", do I need any paper work to fly it
under Sport.

No.



Also, I have a private with an expired medical. Do I need to do any
paperwork or do I need to take any certification flights to fly under Sport
Aviation?

No, you're good to go.