This is a really nice build. Plenty of mechanicals and metal work to keep me very interested! You asked about a smaller roller chain. Diamond Chain makes #47SS, a .1475" pitch roller chain. Should be able to source it through a local bearing house - anyone that carries Diamond chain. See it at
http://www.diamondchain.com. Also,
http://www.pic-design.com and
http://www.nordex.com have this size.
Ken