Re: The #4 movie - which movie series will have it first?
The original cast of the X-Men trilogy is probably going to the past period (where the cast of First Class is set), so Days of Future Past is going to be the 4th chapter of their adventure as the X-Men. So that makes it X-Men 4. They are not showing events that already happened in the past. And its not a spin-off like The Wolverine where there's only 1 character from the original trilogy that is going to appear in the movie in a starring role. This isn't also a cross-over movie like The Avengers because First Class wasn't a separate series.
We can only really confirm that DOFp is X-Men 4 once we saw the movie, but I'm quite confident that DOFP is X-Men 4. Having half of the cast of X3 says it all for me.