upgrade a very large backing store to teamsite 5.5

System

Hello,

I need to do an upgrade of our TeamSite server 5.02 to 5.52.
the first question is whether or not to go to 5.52sp4 since you cannot upgrade to 6 immediately from sp4 to v6.

the second and big question for me is what is the best practice to upgrade our 90 gigabyte teamsite backing store to version 5.52. if I only migrate the last editions which is aproximately 10 gigabyte what is the best way to do this.
I am not allowed to have a big downtime since people need to do updates regulary.

hope somebody has some experience with it and give me some input.

thanks in advance

/erik