Good post. You dug up more evidence than I did.
What I'm curious about is how Papa Raith got ahold of the blood curse that the Red Court set up in Changes (or how The RC got it from Papa Raith.)
I originally assumed Mavra was responsible for Sells, because she seems to have been responsible for training Bianca. But to approach and train Sells, she would have had to used an impressive fleshmask or illusion, simply to approach him.
Raith, if he owned the company, could have met him through work, shaking a hand here and there, and realizing Sells' potential.
So my current theory is that Mavra taught Bianca magic, and Raith taught Sells. The bloodline curse sounds like something Raith would know, since the family is (presumably) Etruscan. If you combine steriotypes like Italian blood fueds and the evident 'honor' inherent in the Raith self-perception, a bloodline curse that would take out an entire enemy family would make sense. The fact that Mavra has been around long enough to learn it also makes sense, especially if she and Raith know each other.
Your theory is quite convincing.
I see only one problem:
I had assumed he was feeding from you and had you under his influence, but after I listened to the security tape from the portrait gallery I was delighted. Both of Margaret's sons. I finally will escape her ridiculous little binding, remove a troublesome thorn in my side-"
Raith didn't know that Harry was Thomas brother. Or he lied.
That opens up more questions about the entire plot. Namely, why didn't Raith kill Thomas the instant he suspected LeFay's curse? According to Thomas, Raith's attempts to kill him over the years were more in line with his standard policy on male offspring, rather than some deliberate attack to stop the curse. So Raith must have just recently thought of the possibility. Which, of course, would invalidate the motivation of killing Harry in SF to remove the curse. But killing a local WC wizard using a cats paw would follow the WCV's profile, and would be beneficial to his Cabal of Evil. Especially if there were future plans for the Chicago area.
Yeah, that makes a lot of sense. Also note that the primary targets were a Red Court controlled prostitute and Marcone's bodyguard -- both entities moving in on Raith's traditional field, lust.
Even if Raith didn't have Maggie Lefay's bloodline curse worked out yet and didn't know about Harry, Victor Sells' actions would be a great way to move against Marcone and the Red Court (I think it's probably a mistake to think of the Black Council as perfectly unified).
I don't see where the 3I is an attack on the Reds. Marcone had a stanglehold on crime in Chicago. The 3I ring challenged his ring, and would have compromised his status. That in turn would have opened up Chicagoland to the Reds. Especially if theres a drug out there that opens new potentials to the Reds. If people get addicted to one magical drug, they'd probably more susceptible to RCV venom. The only way I see it challenging the Reds is that it runs the risk of letting the 3I users to see th RCV's true form, rather than their fleshmask illusion.