I know the Jesus Seminar held that Q and the Gospel of Thomas were prior in composition to the writing of the Synoptics. Is this still a dominant view among scholars (as far as Thomas)? What can be said for or against this view? And under either scheme, do any of the writings have a literary dependence upon one another? How do they relate?
This question is hotly debated, and there's no real consensus. There's a very recent monograph on exactly this topic, Goodacre's "Thomas and the gospels". He argues strongly that Thomas is dependent on Matthew and Luke. According to Goodacre in an interview with his publisher, scholars are divided roughly 50/50 on whether Thomas is early and independent or late and dependent. Goodacre should be well situated to give such an estimate, since writing such a book requires reading the relevant literature, and furthermore his claim is consistent with the wide range of opinions cited at earlychristianwritings. So there certainly isn't a dominant view among scholars, and there may not even be a clear majority view.