Exchange 2007->2013 cert question

I'm about to renew my cert for exchange and after that, I will migrate to 2013.

Here is what I have now:

- my external domain: domain.com
- my internal domain: local.domain.com

My cert is for:

mail.domain.com
autodiscover.domain.com

Because my internal and external domain is different, I'm using the DNS zone trick so my email server is accessible using the same name internally and externally.

- - - - - - - - - - -

My current setup is only one server but my 2013 setup will incorporate 2 servers: I will be using DAG for database availability and DNS round robin for CAS.

MY QUESTION IS:

what do I need on my new certificate ?

First of all, I know it will be 'legacy' name for 2007 server but should it be legacy.local.domain.com or legacy.domain.com ?

Also, since I will have 2 new servers using DNS round robin, they will be both using mail.domain.com name in CERT, am I right ?

Thanks