Magnetic Progenitor if the most flexible allowing you to make pure elements like toxin/heat, and also be used for Profit Taker setups.

Corrosive Heat is for base steel path and starchart against Grineer/Corrupted without armor strip.

With armor strip, swap [Primed Convulsion] for [Ice Storm] or [Deep Freeze] to make Viral Heat.

For corpus, you can either do Pure Toxin (swap [Primed Convulsion] and [Primed Heated Charge] for [Pistol Pestilence] + [Primed Expel Corpus]) or Viral Electric (Swap [Primed Heated Charge] for [Ice Storm] and rearrange order).

For murmur, you can either do Radiation (swap [Pathogen Rounds] for [Anemic Agility] or expel murmur) or Viral Electric (Swap [Primed Heated Charge] for [Ice Storm] and rearrange order).