Ran 4 stacks for the full Early Access Beta, almost exclusively in PvP.
OP covers effectively everything we gathered as well. Great post.
A few notes:
1) Upgrading horde is huge.
2) Prioritize offense on Hockers/Stingers, Utility on Retch/Exploder, and Defense on Tall Boys. All stats are important, but those are the priority ones for best effect.
3) Double primaries is huge -- keep something with lots of ammo/good range in your second slot. If you go down you can still lay down heavy fire for your team and keep them covered to res you.
4) Pills and related cards are OP. Between numb and the crouching card (forget the name) you can get a ton of flat damage reduction.
5) Bomb Squad is a fantastic card -- makes your explosives mow through enemies, and makes you survive accidental explosions as well as Exploders themselves.
6) Have a "medic" on the squad focused on keeping people up. They should be tanky as well.
...