1) You do not need to disconnect the tube from the intake manifold.
2) 2 ft. or so.
3) Cold.

However, I had a difficult time with the speedo cable method. I removed the intake tube that goes across the top of the engine from the filter, blocked the throttle plate open and worked from the intake manifold side into the tube. It is the intake manifold end that gets plugged. I made a curved guide tube from copper tubing and ran the speedo cable through that. You can just see the intake end of the EGR tube when looking down the throttle body.