1- Do cavalry units get Cohesion hits for doing and orderly withdrawal?
They dont take the automatic hit as per 6.72 point 1. But the other points do stand, so if withdrawing from enemy in their flank/rear they will take a hit, and they have to take a TQ check at the end of their withdrawal.
2- I'm not clear how the breakthrough portion of the shock resolution works. A unit which accumulates 3 times more cohesion points and another one adds 2 additional Cohesion hits. Does this mean a unit taking 3x the hits in the current shock? or is it a comparison of current cohesion hit number overall.
For example: Unit A starts with 0 hits and takes 1 hit. Units B starts with 2 hits and takes 1 hit during shock with A. Now they have 1 and 3 respectively. Does breakthrough occur and B takes 2 more?
Yes. It's the accumulated hits, not the ones just earned in combat.