Our current NW65 cluster is only at sp5 with DS

Our Linux server are at OES2 sp1 DS 8.8 sp5 (this is the best I'm allowed here)

On to my question, do I have too (or should I) upgrade the NW boxes to SP8 with DS 8.8.x.x before starting the rolling cluster upgrade? Once I start I expect it to only take a couple days before I switch them all so I wouldn't have a mixed cluster running very long.

Next part is - can I do the Linux part as 64bit? or stick with 32 for now.

Any other tips tricks I should look out for when doing this?