Make sure you use the documentation from Checkpoint.
They have written een excellent upgrade guide to NGX.
Especially the pre_upgrade_verifier (page 59)
And the upgrade paths on page 14.
I think all your questions will be gone after reading this document.
All off the documentation can be downloaden from the checkpoint site.
http://www.checkpoint.com/support/te.../docs_r60.html Regards
Martijn