Re: How should they handle Wolverine in this movie? (if he had to be in it..)
They can certainly switch back and forth between the future and the past just like they did in the comics which is why I think Bishop and Blink will travel back in time.
That way, with those two in the past it'll feel like two new characters added to the First Class team with the story split between 1973 & the future where the returning cast members still get screen time. If you keep Blink and Bishop in the future, they would most certainly get swamped underneath the returning cast members. As I said, this way it gives them character development and importance to the story if they are the time travelers.
That makes the most sense to me.