Cluster Updating with Exchange 2013

I am asking this here on exchange forum even though it has to do with server 2012 but the servers have Exchange 2013 and i DO NOT want updating to mess up Exchange.

Server 2012 R2 with Exchange 2013 SP1. Exchange has 1 DAG with 2 member servers. Exchange servers are hyper-v 2012 R2 VM's. All roles installed on each server. I have not installed any updates to either server 2012 or exchange 2013 since the move over to exchange about a year ago. So now to my question:

1. how do i correctly update server 2012 r2 without breaking exchange 2013?
2. Are there any server 2012 updates that you have experienced break exchange 2013?
3. Do i configure/use cluster aware updating snap-in?
4. If i use CAU, does it matter in what order i apply the updates (active copy vs. passive copy)?

Thanks for any help.