RAD ALT hold on the S76 is not very good, and if you read through the manual I think it says that it is only demonstrated to sea state 3, or something close to that. When you really need the system, you have to do it manually.....
The need to beep forward speed on VEL HLD could be due to doppler is maintaining surface water speed. Depending on what you are trying to hold position on, you always have to adjust this value a little.
CW and CCW is used when there is a lot lot of precipitation in the air. It cuts the doppler wave to avoid misreading. I have never seen any difference in doppler behavior using it.
CB