.. is a major consideration, as well as wireless range if you are broadcasting from an external outbuilding 70 feet away.
Wireless security is extensively covered in other threads on this forum; i.e. look for kit that supports WPA encryption, MAC address filtering, etc.
I went with kit using the same MIMO pre-N technology base. Its multiple-path method helps to ensure _better_ wireless connectivity, but usually with walls to reflect signals off ~ yours are in 2 separate buildings.
So I personally would look at kit which will enable you to attach separate directional aerials which can "point" at each other ~ even for PC2 in the house which also has to transmit back to the router in the outbuilding.
The extra bandwidth will not be necessary if you definitely will only be looking for internet access, no file nor printer sharing, etc.