So... after finally getting my second core I have some left over Ardus and Kari figures and was thinking of converting them into infantry command units. Does anyone have suggestions on which figures would be most useful to have multiples of?

I'd say you'll have the easiest time turning them into champions, since those are pretty much just "heroic figures" and don't need banners or instruments. That said, you'll have to put in a fair bit of work to differentiate them from the upgrade versions of those models - swapping faction might be your best bet.

Someone put a bald head on Ardus (and gave him swords?) and he ended up looking like a pretty good human champion.

I think for Daqan the weapon master guy has good use in multiples. For Waiqar the executioner and the necromancer.

You could probably use the arms off one of the sword and shield Reanimate models and make something close to the Executioner/Saboteur figure

Hmmm I have 3 Ardus's figures, I will look at them tonight! new undead champs coming!