Migrating from Exchange 2003 to Exchange 2010 - Client Access Server Role

We are in the process of migrating from Exchange 2003 (SBS) to Exchange 2010..  We are currently running BES 4 Express and Activesync for iPhones.  The plan is to install BES 5 on the Exchange 2010 server after it is installed and migrate users over, since there's no direct upgrade bath from BES 4 Express to BES 5 Express.

OWA is externally accessible from https://mail.mycompany.com/exchange.  
Sharepoint/Remote Web Worplace is accessible on the same server from https://mail.mycompany.com/remote

If make the Exchange 2010 CAS external domain the same https://mail.mycompany.com, it will break Sharepoint, since it's on the same server.   It will also break Activesync for current users as well?   I'm assuming BES continues to work though?

Can I do the following?

Keep https://mail.mycompany.com for the current server
Make the CAS external domain https://mail2.mycompany.com and externally accessible.

As we move users over to the Exchange 2010 server, we will have them re-configure their iPhones and Outlook to go to https://mail2.mycompany.com.  I'm assumingwe'll have to create a new profile in Outlook, and that it won't just migrate them over.  And, if they have a BlackBerry, we will re-activate them on the BES 5 server after we move them.

Will this option work?