Hex vs. Key

[alysume]

Our team is planning our drivetrain for next year, and we are considering using hex shafts instead of a key, as we have done in previous years. What are the pros and cons of each? I've heard that a hex broach costs quite a bit of money, but that's about all I've heard. Also, how do hex shafts work with e-clips?

A couple more hex related questions:
-When we buy say 3/8" hex stock, is 3/8" the diameter of the incircle or the circumcircle?
-If we buy 3/8" hex stock, I'm assuming we would use a 3/8" hex broach? Would we drill a 3/8" hole, then broach it, or drill some smaller hole?
-We only have a manual lathe. If we wanted to turn down the ends of the hex shaft so that they fit into bearings, is the interrupted cut hard to deal with?

Thanks a lot!