There is a surcharge of 2.95 € if you are 4 people or more.
There is another surcharge of 1 € from the second piece of luggage.
There are shuttles operating between both Orly and CDG airports and Paris.
When you book a taxi by phone, the meter starts to turn from the moment the taxi driver leaves to pick you up, so when the taxi arrives, the meter will already show more than the minimum charge.
Many drivers don't speak English so you it's a good idea to have your destination address printed out.