VMware 4.1 to 5.1 upgrade path

We are upgrading from version 4.1 to 5.1

My VMware setup is as follows:

2 Left Hand SANs - Mirrored

ESX1 (ESXi Host 4.1) HP Server

ESX2 (ESXi Host 4.1) HP Server

ESX3 (ESXi Host 4.1) HP Server
* vCenter64 (vCenter Server 4.1- Virtual Machine)
   64 bit 2008 SP2 - Local install of SQLEXP database

VSA1 (ESXi 4.1, Virtual Server Appliance) 9.0 TB (7 TB for Veeam BU, 2 TB to run VM's on in crisis). HP Servers

VSA2DR (ESXi 4.1, Virtual Server Appliance) 9.0 TB (7 TB for Veeam BU, 2 TB to run VM's on in crisis).  HP Servers

1. What would be the best (step-by-step) upgrade process to 5.1

2. I can do an in place upgrade of the vCenter64 Server and want to retain all             settings and keep SQL on the same server.

3. How do I start the upgrade on the Vcenter64 server (iso attach to CD drive and or use update manager?).  This will have to be done first correct, do I need to address anything with the SSO install?

4. Then proceed to do the ESX hosts 1, 2, 3 individually, same as above should I use ISO or load the ISO to update manger?  Does the Vcenter64 on ESX3 present any issues?

5.  The same thing on the VSA to upgrade them (ISO vs update manager), these are not as critical as since no live data is running on them.

6.  Doing full Veeam backups of all VM's.  Once done I want to proceed to upgrade to 5.1 should I take any other precations before  hand (snapshots, clone etc?)

Thanks

KJ