The wifi is free if you are using a free hot spot or your home wireless network. If you connect through BT Open Zone for example you will have to pay. But the web browser will go the the Open Zone website where it will be quite clear what the costs will be as you will have to pay up front.
It's not free to use GPS, you will pay for the data downloaded to provide a map for the area you are looking at. You might only do this once per area (i.e. once you've got a map of your home town it will stay in your memory) but when search for a route to the Isle of White for example you will pay for every map between your house and the destination to be downloaded
Depends what software you are running. I have Route 66 installed. Ok the software cost money but to use it is completely free unless you want the camera and trafic updates.