In my book you should always be cutting in ProRes with RED. The proxy cutting method is a dicey balance of immediacy and cross-fingered RT trickery. ProRes however is a very solid codec for editing. Plus it plays wonderfully over FW800 from a GRaid.
On top of all that, ProResHQ from RED is exceptionally good looking compression and could possibly be used for finishing if the money and time runs out (it never does that, does it?).
The re-conform process from Log and Transfer from ProRes back to RED is super easy. Just follow the white paper on RED’s support page.
I can’t comment on 6 vs 8 RAM… but you absolutely should have matching RAM manufacturers. Any slight mismatch in speed is going to cause hiccups.