Cross-Forest Migration 2003 to 2010 Resource Forest Steps Review

I'd like some advice on the order of steps I have below (these were accumulated through research, prior knowledge, as well as a support case with Microsoft to go over a migration plan). 

The background is Company A (abc.com) acquired our Company B (xyz.com).  However, we have a newer Exchange (2010) server, so they want to migrate their mailboxes from their Exchange 2003 server into our 2010 server, but keep their user accounts in the Company A domain in their separate forest.  Then, we would become the authoritative email server for abc.com, so we would change all of our current users to abc.com email addresses as well.  Our Ex2010 is currently setup to only send email through and receive from a cloud-based spam filtering service.  Company A still has some Outlook 2003 clients, and I don't think they will all be migrated to Outlook 2010 before the mail migration, so I have to account for Public Folders for Free/Busy.

The steps below are what we've mapped out, but I don't believe they are in the correct order.  I've completed the first 5 steps (green).  I need to make sure the mail flow works during the migration process, co-existing until done, and the creation of the send connector on my Ex2010 was guided by Microsoft support.  They also advised step 9 to configure a send connector on Ex2003 to forward to Ex2010, but I don't know if that needs to be done before changing DNS and MX records?  Should I be creating the send connector on Ex2003 to set up the flow, then changing the DNS and MX records so that Ex2010 becomes the authoritative abc.com email server and THEN migrate mailboxes?  Are there any steps I'm leaving out?

1. Private Connection (MPLS)
2. Create Conditional Forwarders pointing to each other’s domains on the DCs
3. Forest and Domain Trusts - Two-way
4. UCC SAN SSL Certificate with abc.com as common name installed on Ex2010 (services not yet assigned to it, as our current xyz.com common name UCC SAN SSL cert is used)
5. Added abc.com as accepted domain on Ex2010, configured as Internal Relay pointing to Ex2003
6. autodiscover.abc.com and mail.abc.com Internal DNS records pointing to <internal IP of Ex2010> on Company A's DNS before migration
7. Public DNS records for mail.abc.com, autodiscover.abc.com pointing to <public IP for Ex2010>
8. Replicate Public Folders from Ex2003 to 2010
9. Setup Send Connector on 2003 (New SMTP connector – General tab – forward all mail through Exch2010 – Address Space tab = SMTP abc.com and select “Allow messages to be relayed”)
10. Change MX record for abc.com from <Company A> to <cloud based Spam filter IP>
11. Migrate Mailboxes (using Binary Tree E2E) into Ex2010 and they will be Linked Mailboxes to user accounts in Company A's domain
12. Change the Accepted Domain “abc.com” to Authoritative Domain in Ex2010
13. Email Address Policies for “abc.com” for Company B users
14. Change URLS on 2010 from mail.xyz.com to mail.abc.com
15. Manually reconfigure all Outlook 2003 clients to point to mail.abc.com