First off, congratulations on the purchase
I don't think there are any differences regarding the sport or premium packages between the 4 door, 2 door, or convertible. If I'm wrong, maybe somebody else can weigh in?
Anyhow, the sport package consisted of:
17 inch wheels
Sport steeling wheel
12 way power sport seats
Wood grain interior trim
Auto dimming rearview mirror
Rain sensing wipers
Keep in mind it's possible to have some of these options without having the whole package - for instance, you could order heated seats or moonroof w/o optioning for the premium package.
As for maintenance, a lot of people change their own oil and such, but you can't change the service mileage countdown indicator unless you have the computer. As I've read, the computer is quite costly and only the dealer has them. Haven't heard of any private owner possessing one