Sorry for the drive by; I must say this is shaping up to be an absolutely amazing side-mod and if it is anything like the Vanilla 1648 it will be amazing.
That being said, a slight drive-by correction to this. There's at least one and a half examples of an indisputably "Western" nation besides the Knights (depending on how you define it; would the Imperials count?).
That would be the Republic of Venice, which was fighting on the side of the main anti-Ottoman alliance led by the Empire. And in particular fought the Turks for its' last Greek colonies. By the end, it had one last final hurrah as the leader of an alliance with France, the Knights, the Papal States, and various Greek partisans against the Turks, had endured the longest siege in recorded history at Candia (almost as long as the Thirty Year's Proper!) for longer than anybody had imagined, and finally fell apart and exited history's stage while the Imperial-led mainland army drove back the Ottoman armies.
Suffice it to say, there's plenty of food for inspiration there. I'm not sure how you would work it given the faction list (and how the French and Papal troops involved were directly under Venetian command in Crete). But I just figured it would be worth noting.
Other than that, best of luck!