How to upgrade Domain - 2003 to 2012 R2 - task sequence

Question

Could someone please sanity check this task sequence?  I need to upgrade a 2003 domain to 2012 R2 and would appreciate a second set of eyes.  thx.
Goal:
1. standup two new 2012 R2 DCs
2. decomm three old DCs
3. raise DFL/FFL to 2012 R2
Current DFL/FFL = 2003 (one site, one domain, 3 DCs, 400 users)
3 Existing DCs (all to be decommed):
  OldDC1 = Svr2003 Std Ed SP2 x64 (holds all FSMO roles, GC=yes)
  OldDC2 = Svr2003 Ent Ed SP1 x86 (holds no FSMO roles, GC=yes)
  OldDC3 = Svr2003 Std Ed SP2 x64 (holds no FSMO roles, GC=no)
New DCs to be added:
  NewDC1 Svr2012 R2
  NewDC2 Svr2012 R2
Proposed task Sequence:
* build and patch OS, then add ADDS role to NewDC1 and NewDC2 (do not yet add servers to existing domain)
* in the network config of new DCs, set the DNS server IP to the IP of OldDC1
* when installing ADDS, I will be prompted to run Adprep.exe - it will be run as part of installing ADDS - this will update existing domain schema as needed.
* add NewDC1 and NewDC2 to existing domain
* in the network config of the new DCs, set the DNS server IP to that of the local server
* make both GCs, make both DNS servers
* distribute FSMO roles thusly:
* DC1 = PDCE, RID (more frequently used roles)
* DC2 = SM, DNM, IM (rarely used roles)
* run dcdiag.exe commands to verify functionality
* power off OldDCs one at a time, waiting 24 hours between each shut down
* raise DFL/FFL to 2012 R2 after all old DCs are decommed

Answer 1

revised and updated
Goal
1. standup two new 2012 R2 DCs
2. decomm three old DCs
3. raise DFL/FFL to 2012 R2
Current DFL/FFL = 2003 (one site, one domain, 3 DCs, 400 users)
3 Existing DCs (all to be decommed):
  OldDC1 = Svr2003 Std Ed SP2 x64 (holds all FSMO roles, GC=yes)
  OldDC2 = Svr2003 Ent Ed SP1 x86 (holds no FSMO roles, GC=yes)
  OldDC3 = Svr2003 Std Ed SP2 x64 (holds no FSMO roles, GC=no)
New DCs to be added:
  NewDC1 Svr2012 R2
  NewDC2 Svr2012 R2
1. Assessment of current AD infrastructure
* http://technet.microsoft.com/en-us/library/hh994618.aspx
http://blogs.technet.com/b/askpfeplat/archive/2012/09/03/introducing-the-first-windows-server-2012-domain-controller.aspx
http://blogs.technet.com/b/askpfeplat/archive/2013/06/03/upgrade-active-directory-to-windows-server-2012-phase-1-assessment.aspx
http://msmvps.com/blogs/mweber/archive/2012/07/30/upgrading-an-active-directory-domain-from-windows-server-2003-or-windows-server-2003-r2-to-windows-server-2012.aspx
2. build and patch OS on NewDCs; in the network config of new DCs, set the DNS server IP to the IP of OldDC1
3. add AD DS role to NewDC1 and NewDC2 (do not yet add servers to existing domain)
* NOTE: when installing AD DS, you will be prompted to run Adprep.exe.  It will be run as part of installing AD DS.  This will update existing domain schema as needed
4. add NewDC1 and NewDC2 to existing domain, promote to domain controllers, add to existing domain at 2003 DFL/FFL.
5. make both DCs GCs, transfer/distribute FSMO roles
* DC1 = PDCE, RID (more frequently used roles)
* DC2 = SM, DNM, IM (rarely used roles)
* http://support.microsoft.com/kb/324801/en-us
6. verify time service on OldDCs are syncing with current DC1 (PDCE)
http://msmvps.com/blogs/mweber/archive/2010/06/27/time-configuration-in-a-windows-domain.aspx
7. run dcdiag.exe commands to verify functionality, address any issues
8. Make new DCs DNS servers
* in the network config of the new DCs, set the DNS server IP to that of the local server
9. retest with dcdiag
10. decomm OldDCs
* reconfigure clients/servers so they no longer point to the OldDCs/DNS
* disconnect network cable from old DCs and test with various clients, reboot clients, retest
* remove GC from old DCs, (also remove DNS role?), then run dcpromo to demote them
* verify that OldDC machine accounts have automatically moved from the DCs OU to Computers container
* check DNS management console in NewDCs, verify all entries from the old DCs are no longer present, delete manually if nec'y
* check AD sites and services and delete the old DCs if nec'y
11. raise DFL/FFL to 2012 R2 after all old DCs are decommed