1) I doubt Fenharel will play an actual role or in anyway be present or connected to events in DAI. If he is, he will either be a fade spirit or someone impersonating Fenharel. Sorry, the entire MO of DA and its plot so far has been to be extremely vague on the existence or dieties of any kind. Sure we have the ashes, but that in no way proves that there was a maker or that there is anything special about the ashes given the huge lyrium vein that is present. So I seriously doubt there will be any role played by Fenharel, at least as any kind of actual God.
2) I think the Dalish presence in the game will revolve around the Arlathehven they are having and will possibly impact some of the dalish future but will definitely give us a bigger glimpse of Dalish Culture.
3) I am not certain how big of a plot piece Briala and company will actually be. Could she be a big guerilla presence and all that? Possibly. She could also be just a shadow group that is helping the city elves out but is not yet a major player on the level of Celene and Gaspard. We truly have no idea how developed that plot line will be in DAI. Especially considering there is no CE Inquisitor.
4) Speaking of Celene and Gaspard...I entirely expect the possibility of reconciliation to be there. Not convinced it will be a possibility, but the way the two characters are written as pragmatists and devoted to the Empire, just in entirely different ways, I could see a reconciliation to save the empire as being possible. Especially since neither of them are portrayed as despicable or even truly unlikeable.
5) The romantic in me would like to see Brialla and Celene get back together, the realist in me though can forsee them working together, but I doubt they ever have a relationship again.