Deploy exchange 2013 with current Exchange 2007 organization

Question

Dear All
    our company will update exchange 2007 to exchange 2013, on AD site we already update Forest functional level and Domain functinal level  to Windows 2003 ( can not up to windows 2008 yet because have some ad that run windows 2003 server
) but one thing that I'm not sure, between migration we can not full tranfer mailbox form exchange 2007 to exchange 2013 in one time, we need to migrate on night time manybe one day we can migrate only 100 user per night, my question is
1. which exchange 2013 server role that we will install first ( mailbox or CAS)
2. on migration time, can we let's user used exchange 2007 to main of OWA and SMTP or not? we need all user's mailbox tranfer to exchange 2013 complete first after that we will switch OWA and SMTP

Answer 1

1. Mailbox, or install both on the same server at the same time.   (Edited:  First I said CAS, which used to be true, but now you need the Mailbox role to run PowerShell, so you have to install Mailbox first.  Consider a dual-role server,
however, because there aren't a lot of cases where you need separate CAS and Mailbox role servers.)
2. You cannot.  Exchange 2013 mailbox users must use the Exchange 2013 CAS.  You can have users use their respective CAS while migrating, but that requires two sets of URLs and is therefore more confusing for the end user.  I recommend planning
to deploy Exchange 2013 CAS, a legacy URL for Exchange 2007, and switch your hostnames to Exchange 2013.  This is all spelled out in the Exchange 2013 documentation.
Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."