The next couple of seasons will combine books 4 & 5 because of the parralell timelines of book 4 with the first half of book 5. However this particular season is just the second half of book 3, so that doesn't really play into it here. As far as Dontos, he is important to this part of the story, but really he should have already been involved by the second half of last season, they have delayed him so I think he is going to be really minimized. The next episode (possibly crossing two episodes) will be covering the wedding, and so Dontos at least massively changed, if not nearly totally minimized, because there should have been alot of him before now at this point.