I'll be using the Legionary Kill Team (gasp!) to represent my very loyal Fire Claws Adeptus Astartes kill team. There are three main reasons for this:

• No Primaris. It's not that I'm against Primaris. It's just that I'm representing a kill team from the Chapter prior to the introduction of Primaris.
• Librarians. The Fire Claws are known for having a large and influential Librarium and I want to include a battle-psyker in my kill team.
• Daemon weapons. The Fire Claws collect and, more importantly, use the relics of Chaos in battle.

Models will accurately portray loyalist Adeptus Astartes, but will follow the rules of their traitorous brothers. I'll probably make datacards for each model (once I get them done and photographed, that is) so that I can use them in games without getting too confused. They'll be accurate to the official Legionary Kill Team, so usable in games, but they'll be re-named proper loyalist names. In the post-Captor of Sin Fire Claws, this is a Quæstor Squad - a squad jointly led by a Sanctifier (see below) and a Lexicanium and tasked with the covert recovery of Chaos relics.

Here's the tentative roster (actual Legionary Kill Team rules hidden - just highlight the grey bars to read the text).

Sanctifier Skeptukhos armed with a bolt pistol and crozius arcanum

Legionary Aspiring Champion armed with tainted bolt pistol and power maul

A Sanctifier is a cross between a lieutenant and a chaplain, a pre-Primaris precursor to the Judiciar. The Sanctifiers are the members of the Chapter tasked by the Conclave with recovering Chaos relics. While the Sanctifiers don't practice vows of silence like Judiciars, I'm going to model this guy so that his mouth is covered, evoking the concept. The "crozius arcanum" will be more mace-like.

Lexicanium Vrotoktónus armed with a bolt pistol and force dagger

Legionary Balefire Acolyte armed with a bolt pistol and fell dagger

Honored Brother Adámastos armed with a boltgun and bearing an Icon of the Emperor Enthroned

Legionary Icon Bearer armed with a boltgun and fists

Honored Brothers are a special type of standard bearer in the post-Captor of Sin Fire Claws, the Icon of the Emperor Enthroned serving to bolster the faith and zeal of the Fire Claws battle-brothers.

Veteran Brother Phriktós armed with a bolt pistol and eviscerator

Legionary Butcher armed with a bolt pistol and double-handed chainaxe

Veteran Brother Megasthenes armed with a heavy bolter

Legionary Heavy Gunner armed with a heavy bolter

Veteran Brother Oplophoris armed with a boltgun

Legionary Warrior armed with a boltgun
 

Each of the models will have purity seals, representing the fact that they have been tested for purity by the Conclave and have been found to be suitable to the task. These are most definitely loyalist Space Marines. It's just that the [Heretic Astartes] Legionary Kill Team rules give me the tools I need to accurately represent the team as I envision them.

In the back of my head, there are plans to expand this to include other members of the Legionary Quæstor Squad Kill Team. The Anointed would be a Veteran with a lightning claw and the Shrivetalon would be a Veteran with a bolt pistol and a pair of power blades. The Chosen would be the most interesting, simply being the same character as the Sanctifier (Aspiring Champion), but replacing his power maul with a daemon blade (I have some Bloodletters and one of those may sacrifice his blade to the Emperor's Angels). I would avoid the reaper chaincannon, but most other things have loyalist counterparts.