@AK, if you have a separate domain name inside and out (like at Microsoft - you email to @microsoft.com, but internally everything is built on a corp.microsoft.com basis), then you might need to have more names in your list. You would certainly have to think about that. I will be using a split DNS so that my users, internal or external, will use the same names to get to OWA (for instance).
As for the NetBIOS names (or short names - meaning names like "CAS01" rather than "CAS01.robertsrules.ms")... You would only need those if users will be accessing services by those names directly. When Exchange accesses names (through proxy for instance), or tells the users what names to access (through redirection, for instance), it will always you a FQDN, not a short name. There are some situations that would require the short names on your certificate, but we will not be doing those in Robert's Rules, and you can almost always get away without having to do them anyway.
Thanks for the questions - both very good ones!!