The 254 conveyor slideshow goes over a lot of what you're looking for. McMaster sells polycord (we usually use the 3/16" OD):
http://www.mcmaster.com/#round-belts/=zsnxr5
We love polycord, especially for rollers, you can cut and weld it together in a few minutes, and it's super easy to replace. It is also good to use polycord in applications where come slipping is need or expected, mainly so you don't strip a timing belt.
Most rollers we use are polycarbonate tubing with a machined or 3D printed hub that is inserted into a bearing which then fits a into a plate. The hub is then riveted onto the tube.
For pulleys, we usually use custom machined "rope" pulleys with a hex or round keyway bore. We last used poly cord on our 2014 robot roller.