Cascadia Flare was built for this weapon. This thing can max out flare stacks in under a second with 0 kills, and maxes out at higher peak damage than any of the other arcanes.

• At 0 Kills. 40 max cascadia stacks. Averaging 19 heat procs per second per target = 2.1 seconds for full ramp up on a single target or 0.7 seconds for full cascadia ramp up with 3 targets.
• Any stacks of [Galvanized Diffusion] will speed this up even further, capping out at: 27.5 heat procs per second per target = 1.45 seconds for full ramp against a single target or 0.48 seconds against 3 targets.

Candidates for Riven mods are Deep Freeze and Pathogen rounds, focusing on ensuring you get a matching element + crits/multishot along with one of the many many negatives which do not affect this weapon. (Max Ammo, Zoom, Impact, Slash, Puncture, Projectile Speed, Recoil).
An ideal Riven Mod has both Cold + Toxin + crit/multi/fire-rate and a negative with no harmful effect. This way you drop both [Deep Freeze] + [Pathogen Rounds] and replace them with your riven + an expel mod. However, this isn't strictly necessary because this weapon absolutely melts everything without a riven or expel mod.

Melts everything in steel path even without a primed expel mod.

(Magnetic is a half decent alternative for the Kuva element.)