No. The K80 is a Compute-only device from NVIDIA (i.e., it won't run OpenGL or DirectX). We've previously announced that cards with Display are coming "soon".
Actually, the K80 does run OpenGL. Source: I'm building a remote rendering solution that runs on a couple of K80's, and it works just fine.
No, but there are guides out there to use SteamLink for gaming on EC2.