Unfortunately I have no insight regarding Sorcerer or Druid class so can't offer any suggestions about those two classes, but if I was making a Dark Urge thematic build I'd personally go with Dexterity Tiger Barbarian dual-wielding daggers and multiclass into Rogue. That way;

  • The Barbarian rage would fit Durge's urges aspect as in gameplay, dialogue and roleplay elements
  • You'd be able to make enemies bleed a lot which fits the sanguine theme
  • As a Rogue you'd also have the roleplay elements of being sneaky and knowing the underground, which fits Dark Urge's lore
  • And Durge really loves its daggers so that would further fit the sanguine theme of who they are

As for companions; I personally went with Shadowheart, Lae'zel and Minthara in my evil playthrough because manipulating them two down the worst path imaginable to corrupt them is far more fun in my opinion, which is why I made Shadowheart and Lae'zel evil fanatical zealots of their own gods and eternally enslaved them afterwards.

(As for Astarion)
I don't really like having him for an evil playthrough because he loves the evil path way too much, so instead I kept filling his head with hopes and dreams of being free... before giving him away to Harleep to suck his soul out and bind him as her eternally mindless sex slave grin