Nice to see another person from the Twin Cities here.
I use Fomapan 100 for pinhole. It has terrible reciprocity, which is great for pinhole photography (in my opinion).
Sharpness and contrast is something that is greatly determined by the quality and the roundness of the pinhole in your camera, and the Zero is really good. By using Acros you have one of the sharpest films available to you, and almost any other film will be less sharp, Fomapan 100 included. Another good film is Ilford Pan-F+, which is a little grainier than Acros, but also easily develops very high contrast.
Enlargements at 12x12" from 6x6 pinhole is never going to be sharp.
Nice to see another Minneapolis person here.