I have a similar project in the works - really wanted the look of a cowhorned single speed but with at least 3 gears. With everything I read on the sloppiness of the various internal hubs, I'm choosing to go with a new Shimano Nexus red band 8 speed combined with a Miche Primato crank. Really wide range of gears and you can set it up with or without a coaster or a roller brake. I'll be going with standard calipers though.

Good luck on your project.

55/Rad