Cool with Kraeger Antal, Brenard Volkstan, Ferreus, Bethuel Cortexus, Lyras and Kurak; all of those are good to go.

I'm not feeling a Raven Guard in this scenario, and Merdem Jercul's bio is really underwhelming in comparison to the work everyone else has put into the character sheets. It doesn't have any real context that explains why he'd abandon his legion before Istvaan III and it's actually somewhat out of touch with the subsequent events of the Heresy as well. Since the Raven Guard was shattered at Istvaan III and engaged in an extensive guerrilla campaign, the character wouldn't have to actually have left his legion in order to fight.

The backstory makes little sense.

As to a Praevian, I was going to suggest a techmarine, but realized that one of those would spazz out at the sight of the pariah wargear. I'm not sure I want to go there, preferring to stick to a fairly stock Space Marine type and depending on the player to distinguish them that way.