Upgrade Server 2003 Std & Exchange 2003 to Server 2012 R2 Std and Exchange 2010

This scenario is not supported totally
There is no direct upgrade path available to windows 2012 from 2003 server
http://technet.microsoft.com/en-us/library/jj134246.aspx

Again inplace upgrade of Exchange 2003 to 2010 is not supported
You need to install seperate box with 2012 as a member server and need to deploy exchange 2010 in Co-existence scenario with Exchange 2003
Later on you can transition from 2003 to 2010
Please check below nice guide for steps involved and prerequisites as well.
http://exchangeserverpro.com/wp-content/uploads/2011/02/Exchange-Server-2003-to-2010-Migration-Guide-V1.3-Planning-Chapter.pdf

You don't really have a direct "upgrade" path. If you read through this link it explains how you will have to do multiple upgrades to get to Exchange 2013 or export the PST files and import them into the new Exchange:

http://www.infoworld.com/d/microsoft-windows/you-cant-migrate-exchange-2013-207258

What I would recommend for Server 2003 to Server 2012:

http://social.technet.microsoft.com/Forums/en-US/da2ecaae-a3b8-42e5-bdd3-54370808bd37/upgrademigration-windows-server-2003-32-bit-to-windows-server-2012

If it was me I would build the two new servers and then move everything over to them. The problem is you have waited too long to upgrade and now you are trying to take two steps at once. Build you server 2012, migrate Exchange manually, migrate the FSMO roles, demote your 2003 server.

While one answer talks about coexistence, and another talks about exchange 2013, both miss a fatal and basic answer.

NO version of Exchange is currently supported on 2012 R2, so migrating and coexistence is simply not yet an option, and no guidance can be provided except to wait for support via a future exchange service pack.

I misspoke. I meant the single box will be 2012 dc, not 2012 R2.  with Exchange 2010sp3.  Any good migration instructions for this? Thx for your comments and help.