You'll have a good time. If you're planning on using the tram, subway or any buses, I would suggest buying a multi-ride card. The concierge at Grand may help you, I believe there is a convince store on the corner of the hotel that sells those cards. As I hope you are aware of, Oslo is expensive, and a ride around the corner with a cab will probably start on about 15 dollar in the daytime. Limo service is pretty limited in Oslo.

I don't live in Oslo anymore but I visit regularly. As a tourist, you won't need a rental car, which also would be really expensive in Norway.