That photo isn't enough source material to create an environment map with... The photo contains back-lit hills and trees... so the opposite side of your cube needs reddish front-lit hills and trees, and the adjacent sides need side-lit hills and trees. If you wrap back-lit trees around your whole cube, it's going to look…
yes and no, basicly ao should only appear in the not directly lit parts of the world, the ambient lit parts as the name says so basicly if you want to do it right you should have it as an extrapass and mask it with the lightmap to enhance the shadowed parts and not dirt up the directly lit parts