How long of a tether cable can we use between the RC and OI?
25ft. maximum. 25ft tether and program/debug cables are available for online ordering.
Is the tether cable just straight through? pin1 to pin1, pin2 to pin2, etc?
Yes, the Tether cable is a straight through pin to pin cable. Pin 4 and 6 are not currently used at this time but you should connect all pins.