For the Tanith, I'd go for squads of Imperial Guard Veterans with Forward Sentires (camo-cloaks). If that's unavailable, I'd go for a Platoon Command Squad with attached Commissar with Plasma Pistol, and then five Infantry squads; a flamer/sniper in four squads, a Sniper and Missile Launcher/Autocannon manned by one guy on a big base in the 5th (Larkin and Bragg), a Heavy Bolter in one squad (the stubber crewed by the two hive-girls), and then a mix of Heavy Weapons in the other squads.
Also add a Lord Commissar with Camo-Cloak and Power Sword. Fluff-wise, they all have their own which is what provides the Stealth, but in game that's not an option so you'd have to run it as an attached Lord Commissar for the buff.
Oh, and take Marbo for Cuu, Mkvenner or Eszrah.