Can anyone kindly tell me if I can hook an Apple TV up to a television (in this case at a cottage with no wifi) and then watch content AirPlayed from my iPad that is tethered to my iPhone using the Personal Hotspot?
Obviously the hotspot works watching on the iPad, but I'd like to stream to the TV.
Thanks
You have 2 intertwined issues: streaming from your device to the TV, and getting content to the device to begin with.
You don't need a router, tether or anything like that based on your description. It is simple:
Cellular Service -> iPhone -> Apple TV -> TV. Only one cable needed - HDMI from Gen2/3 Apple TV (RGB available from first gen as well)
Tethering will not have any impact on your data usage, any more than pulling that same data via your phone directly - it all goes through your phone - the tether does not cause any duplication of data transfer. In one case your phone is both the "modem" and the "computer" all in one, and in the tether example you simply use the phone as the modem and the iPad as the "Computer".
Also not sure where you got your per hour download rates, but it will all depend on quality of what you are streaming. Netflix is pretty standard at up to 2 GB per hour from what I've read....