You could change the riven to something like a faction damage mod if you desire or something cool like [Magnum Force] which should make it seem like a [Split Flights] mod or a shotgun.
You can add an arcane if you want or can.
The heat elemental is for added damage and if proc it can serve as a damage dealer and armor stripper but it wont really come in handy so you can change it to another elemental/damage mod if you want.
Gal diffusion and lethal torrent serve there purpose to add damage and have more chances to crit/proc, and with the 100% accuracy (unless you put on mods that decrease accuracy) they should stay in the same path and not veer off like shotguns or split flight bows, which means you should get full damage every time (not counting damage reductions on enemies).
And [Lethal Momentum] is to account for that throwing knifes are SLOW moving projectiles.
And all of that with only 6 forma.
k bye.