I'd be concerned about Russia taking that border province from Crimea, better for you to go to war with Crimea first if at all possible to prevent them from losing any of their eastern provinces to Christians. I guess the OE will have something to say about that though.
That province is my main target. It is a volga tartar culture province, so I would really like to have it, and it would be a good attrition buffer for a Russian attack. Plus also Kharkov, leaving Crimea with their southern provinces. Other targets are Shirvan and Nogai.
One good thing about Ottoman Kazan is that it will either stop Russia from expanding or end in a bloody Russian-Ottoman war in which you can profit from both sides weakening.
A bloody Russian-Ottoman war in the Siberian winter would be perfect!