The only thing I would change is the villians, since the Bulats were used in the last movie (and I can't think of a single plausible reason why HS would release Cristu nor whether or not Tiberiu even survived the final fight scene).
My suggestion for their "stand-ins" would be John James Toomey as Tiberiu, Shauna Toomey as Vera, and their bodyguard (in the film) Barracuda as Cristu. You could retain the whole "Tiberiu assasination" storyline by having that be planned by 'cuda and Shauna, who are having an affair. Barracuda's mercenary background could explain how they have connections to Eastern Europe Slavery rings. Besides, Slavers didn't have a lot of great fights. If you add Barracuda in the mix, you can have a Frank-Barracuda one on one fight when 'Cuda finds his guards drugged, and following Cuda's torture/death, you get the firefight with Toomey and his men when they come for 'Cuda.
Michael Jai White as JJ Toomey
Tiny Lester as Barracuda
not sure who'd be good for Shauna