freitasm:
The other bit of the question is about WiFi area and it is known that cheap extendeders cause more problems than a thought out solution. Also costs make really hard to cover a large area. You should concentrate on where you spend most of the time.
Not to mention 20 acres is a large area to be covering with WiFi - realistically WiFi will work up to maybe 100m or so to a portable device such as a laptop or mobile. To cover such a large area will require multiple WiFi access points which given the description of being "in a valley" may be challenging.