J1939 Wiring Considerations
1 and 3) These are roughly the requirements of 1 Mbps. At lower baudrates you can use longer length and longer stubs. See recommendations from CAN in Automation for industry standard recommendations (the physical layer of CANopen and J1939 is the same).

4) Indeed, it isn't standardized. Here's my theory of why green and yellow are de-facto standard:
What is the color code for CAN Bus?