Bismihi ta'ala
This question is similar to many other fiqhi questions, where one would need to refer to his/her Marja' taqleed.
That being said, according to the view of most of our esteemed jurists, Ahlul Kitab are not najis, and as for temporary marriage with a Kitabiyah woman, most Maraji' also deem it as halal.
And Allah knows best.