Who should lead my Arbites against a suspected Heretic Astartes Chapter?

I'm playing a game of 9th with crusade-like rules and I'm wanting to play an Astartes Chapter vs the planet's Arbites, each thinks the other is corrupt and both of them are half right.

To give the Arbites a bit better of a chance I'm going to run them as Sisters of Battle and say that this planet has an extremely lucrative resource trade that they use to kit out their Arbites with the best gear.

I've got Subductors already and I plan on getting a Combat Patrol to build Subductors and Vigilators to run them as Sacresancts and Sisters of Battle (with shotguns) vehicles are going to come from the Astra Militarum with a Leeman Russ and a set of Field Bombards.

But where I'm not sure is who should lead the detachment?

Later on I might be running some type of proxy mech as Mortifiers which could be interesting with a Morvenn Vahl proxy as the Warlord.

Maybe a Cannoness? Not proxied, just a representative of the Ministorum because bolter bitches are still badass.

Or if I wanted to go really extra I could build a proxy of the Triumph of St.Katherine? Take the extra bits from the Arbites Combat Patrol to build a scene of a relic being guarded while its transfered.

Let me know what you think and if there's anything else you'd go with instead.