Exchange 2010 Hybrid servers and datacenter migration and cutover

Current Setup

1.       Currently Exchange 2010 is in Hybrid setup with Office 365 (Version 15) in Datacenter 1. This does not have any DR datacenter.
2.       New Exchange 2013 servers have been introduced in same domain and forest and in the existing Exchange 2010 Organization.
3.       Exchange 2013 environment has DR datacenter. And Exchange 2013 user all old excahgne 2010 certificates and namespace for OWA, Outlook anywhere, Activesync and also for Autodiscover.

Name Spaces are

1.                    OWA – Webmail.company.com
2.                   Outlook anywhere – External host name – webmail.company.com
3.                 Activesync – mobile.company.com
4.                 Autodiscover – Autodiscover.company.com
   1. But still Hybrid configuration wizard is yet to run from Exchange 2013 servers.
   2.       There is no firewall or any restrictions between any of the Datacenters.
   3.       Exchange 2013 has been installed and all urls have been configured for all above urls.But still DNS change/cutover both in Public and internal has not been done.
   4.       Both Exchange 2010 and Exchange 2013 has been installed with Edge servers and the edge servers also configured using same name space – edge.company.com
   5.       ADFS and Dirsync are already ready and configured they are working perfectly.
   6.       Currently we are able to see free busy information between Exchange 2010 and2013 from the mailboxes which are in both Exchange 2010 and Exchange 2013.
   7.   And unable to see free busy of Office 365 mailboxes from Exchange 2013 mailbox because we have not configured Hybrid on Exchange 2013.Hope our assumption is correct.

Our Plan to Migrate

1. First give DNS name space cutover defined in point 3 above (Not the edge name space) to Exchange 2013.I believe that this will not affect the existing federation or free busy information between Office 365 and Exchange 2010 as Exchange 2013 is also in same Exchange Organization. Please correct me if the assumption is wrong.
2. After 2 or 3 days run through the Hybrid wizard in Exchange 2013 to change the entire mail flow from Office 365 to Exchange 2013.This is the grey area where I am not pretty sure what the changes it is going to create. How it will affect the existing setup. What are the precautionary steps to be followed before doing this process? Because I believe it will modify the existing send and receive connectors which are currently pointing to Exchange 2010 also create new connectors in DC2 through the Exchange 2013 and edge servers.
3. But there is no idea how to have a parallel DR Hybrid setup to co-exist along with the existing or new Hybrid Production servers in DC2.
4. Please let us know if there is any better way to migrate seamlessly without affecting the existing setup like co-existence migration. Because this seems to be a big bang approach which might or might not work. We tried to follow the Exchange deployment setup, but it is not dealing combined with Exchange 2013 and Hybrid parallel cutover in single document.

Regards, Ghouse