1) It really depends on your build. If you go Venom spam, MasterMutangens is the way to go. If you play on Talos I still like ExCreations because of that +1S. With more Wracks, DarkHarvest it's fine.
2) Ossefactors if I'm going to embark them. Otherwise..nothing. I'm not an huge fan of Hexrifles.
3) In a VenomSpam only. I have a list with 8 Venoms+3Ravagers+2Razors to try. All Venoms have DT+MM and 5 Wracks with Ossefactor embarked. All or nothing. Under 7 Venoms I would prefer cut them off and switch on Raiders.
4) When I play them, I use them with 3 Ravagers. That brings more threats on the table, where even if the Oppo needs to focus on Rava, 3/5 DT Raiders still a threat for him. Yes I embark something there (even Kabals are fine).