The kit pistons are kind of a joke, but fortunately the upgrade ones are pretty cheap. You can also use AE ones with no issue.
I use grease on the build, the biggest reason is that if all the voids in the o-ring cartridge are packed with grease then oil can't leak in from the top.
On rebound, for me it's all track conditions. If I need some more pop off the jumps I run rebound.