Certificate Management in Exchange 2013

Hi There,

I need clarification on Exchange 2013 certificates.... In my proposed Solution there are 12 physical Exchange 2013 dual role Mailbox + CAS.

Question:-

1. Shall i go for SAN based certificate of individual certificate as i have Exchange 2010 running in Exisitng environment?

Individual Certificate means ( Owa, Autodiscover & Legecy)

2. I can set Certificates on all CAS servers using single certificate.? Do i need to purchase 12 Certificates or Single certificate would work?

 Thanks,

Amit kumar

Amit