I have several servers that I will be upgrading in the near future. I will do one hardware migration, but the remainder will be an in-place upgrade. I have been reading about upgrading components first before upgrading the OS. Can I get a clear map of what should be done?

On the migrating server, it contains:

Groupwise PO & MTA 6.5.0
Bordermanager 3.7sp2
NDPS Manager and Broker

Should I upgrade the server first then upgrade GW & BM afterwards or Visa Versa? What would be the best strategy?

I should be able to upgrade straight to 65sp4a correct or will I need to bring the servers to 6sp5 first?