I used 3/16" for beer line, and have about 6' to the faucets. This is where the length matters, to provide some resistance for a slower pour, to avoid foaming.
I used 1/4" for gas line. No extra is required past what is handy to remove the keg from the frig, to remove the quick disconnect.
I set my reg to about 14psi. Pressure is related to serving temp and type of beer, but for general use on most beers, people use between about 11-14psi; personal preference is also to be considered.
Check the handy Sticky for other info on Kegging, at the top of the Kegging Forum.