I still create a plane and make models from that. For almost all my modeling needs. Just search for lowpoly modelling and you'll find plenty of attempts on how to create geometry. Pick your favorite
This is a watch for the character I'm currently working on Smooth shaded Weighted normals Wireframe of tris. Had to add this bevel because my lowpoly couldn't catch the bevels in that area even after I manually adjusted the cage in blender UVs Normal map(smooth shaded)
This could be the lowpoly affecting the AO casting... try setting the lowpoly to not cast shadows. http://wiki.polycount.com/AmbientOcclusionMap#Object_Properties_Method
xNormal? Then I would bake with an external cage file (inflated, smooth-shaded lowpoly). I thought the screenshot showing the projection errors was from Painter.
simple thing, your mesh is too lowpoly your faking smoothness with normalmaps but your mesh is still as lowpoly as the unsmoothed version would look like, so how should the raytracer cast the shadows, if not based on youir lowpoly mesh