Noisy A/C belt

[fangbosun]

Hi! The A/C belt on my wife's 3.0D screeches when starting up from cold. You can see that the A/C pulley is not turning when you turn the A/C on. It goes away when you rev the engine and the pulley starts to turn and once the car is warm it doesn't come back. My local mechanic (who is not a BMW specialist....the nearest is 250 km away) suggested initially changing the belt.

What I'd like to know is:

1. is there only one belt (mine says it's a 4PKO810319K4). If there is more than one I assume it'd be better to change them all? Is there a better brand of belt to get? I have read on previous posts that the OEM ones are better than Continental?

2. Is there anything else I should replace while he's replacing it/them. It has done 153K kms.

Cheers