Chakkhurr shots have forced Impact procs, meaning all your shots get the 70% Chance of Slash from [Internal Bleeding].
[Internal Bleeding] will only roll ONCE per damage instance, so increasing chance of proccing Impact will do nothing when the weapon already has forced Impact procs.

Toxin bonus for Viral with just Primed Cold.

PFast Hands is a flex slot, options for that slot:
Riven, if you have one.
PFaction - High damage increase, with the downside of only working against a single faction.
PFast Hands - Mainly for convenience, reducing the painfully long reload.
Galvanized Scope - Very high damage increase, but conditional. Only recommended for long missions where you know you can keep it active constantly.

Riven stat priority: CD > CC > Dmg > MS > FR = Reload