To answer my own question, the 6* gate is pretty easy, just one shot it. Team was:
(L) Rouche -- meirith pearl, magical device
(F) Sareas -- medulla gem, steeple rose
Kuda -- oracle bangles, war demon blade
Afla Dilith -- demon igniter, vorpal chainblades
Xie'Jing -- skyharbinger, enhancing device
Nick -- guardian shard, medblare
I only went to rank 1 SBB, which ended up being good enough. I didn't have mitigation, and every round took at least 2 turns to kill, but enemies were cursed a lot, so they didn't hit hard. Only water, dark, and earth gates left. Water and dark I don't see a problem once I actually try them, but I have like no dps buffing units for earth except Avani for spark. Not sure what I'm gonna do for that one.
As for unit of choice, I claimed Rouche today. As much as I wanted Nyami, the announcement about Krantz getting an omni sealed the deal. Krantz already does dark/light/heals/cures/mitigates, and I'd bet money that one of his omni skills will be to add status negation to his toolkit. That means he has a lot of buff clash with Allanon. Rouche would fit in that team perfectly. Between Rouche and omni Krantz, that covers all elements/crit/critdam/statuses/mitigation. Then you factor in Sirius's omni coming soon, and that covers bb atk, stats, and a solid team leader. Add in omni Eze and you have virtually every buff covered with a slot still left over for whatever you want (pure nuking, more BB support with atro, whatever) and the friend slot is also completely flex.