Author Desperado build. Havoc 40+.
 Hive Scum Build - Warhammer 40k: Darktide 

1.with cooldown stimm you have to wait for desperado about 20 seconds, you can pump it up further with additional rending but stimm won't be aviable every time desperado goes on cooldown. 
2.shoot bazooka into packs of elites. 
3.can swap and pick certain talents to your liking. quick and deadly/sticky hands for blessed stimms as example. that is, if you are on blight spreads modifier and there is no zealot/second hive scum on your team. this is a selfish little fuck route but if you know the game, it does not matter.  hyper critical  (if you are addicted to it), the sweet spot (for infantry autoguns gameplay), pocket toxin are options too.
4.gunslinger improved aura  or ruffian aura is debatable. I like first because of shared ammo you can  further abuse vulture's dodge during desperado cooldown. well, your slaves get free ammo that's cool too I suppose.

REGARDING GRENADE PICKUPS, CONSIDER INSTALLING (INSPECT FROM PARTY FINDER) MOD AND PICKING TEAMMATES WITHOUT BLITZES THAT REQUIRE THEM TO STEAL GRENADES THAT RIGHTFULLY BELONG TO YOU. 

REGARDING TARGET PRIORITY, IT IS ELITES AND SPECIALS. IF GOT NOTHING BETTER TO DO OR IN PANIC -> MAGDUMP INTO HORDE. DON'T BE AFRAID TO SCOUT AHEAD WITH YOUR INSANE I-FRAMES ON DODGES AND DESPERADO BUT BE MINDFUL OF MONSTROCITY SPAWN TRIGGERS.

HAVOC TEAMMATE PRIORITY
1. Veteran (free grenades and gold toughness)
2. Psyker (generally broken character, but not many good players on this class)
3. Hive Scum (if your homie knows the ball, go all in. The more the merrier)
4. Ogryn and Arbiter (two delicious meatbags that can wait out the heat without dying while you are sweating your ass off)
5. Zealot (if you think you need book bot/boss killer or you are on blight spreads modifier)
6. Skitarii (who are you, man)