iPad questions

The cellular model allows you to use cellular data if choose to. You don't have to if you don't want to however.. If you want to be able to use cellular data when away from WiFi then you need to pay for it. I don't know of any cellular service provider that offers cellular service for free.

You can of course not use the cellular service and then you would not have to pay for it. But then there's not much point in paying extra for the WiFi+Cellular model if you aren't going to make use of the cellular hardware.

Only if you purchase a cellular data plan for that device.

Yes. your carrier would be the one to tell you how much the cellular plan for the iPad would cost with them.

Different carriers would have different prices for it.

Meshoo