From CDG to town. Do not take a taxi, it can be very expensive. There is a bus RoissyBus which will bring you to Opera which is in the center. If you just have a carry on you can take the RER which is located opposite to T2 A (where AA is) you will have to keep the ticket because you will need it to exit or to transfer to the regular subway.
Best area to stay Le Marais (4th) avoid the 15th, 16th far from everything. The 8th (Champ Elysees is expensive).
If you have a drink in a cafe, it is always more expensive to seat at a table than be at the counter or sit on a stool by it.
A lot of people speak English now.
Bon voyage...