This will be 4v4, not 6v6. I do much prefer Nucleus over Viaduct.
I would rather stray away from stock maps because people who play them a ton end up having a competitive advantage over those who have never played/plays little. I think a random map or a pub map would be best for our purposes right now, though I'm fine with regular maps. Maybe we can play something more competitive later (I would love to eventually play a highlander match with GHers), but for now we have a largely varied skillset, so a random pub map over something competitive, I think, would be the better choice.