If you leave the airport before 7 you should be OK, 30-45mns to go downtown, but over 1 hour if you leave around 8 is standard. Coming back at 9... that's during the rush hour
although on the way to the airport once you reach the highway the traffic is much better. I would count 2 hours in the car for both ways to play safe, and more if you get delayed at the airport in the morning. Most cafes will be open once you reach town so croissants are a safe bet. Actually the taxi tour sounds like a decent option (it's abt 50 E 1 way including standard traffic jams and 50-80euros extra will allow you a tour downtown. And downtown with car in Paris is *very* scenic if the driver doesn't have you stuck in some small streets.