Who is that? Where it all happens?
I think it's
And it all happens, of course,
Every picture references the title of one of the HP books, or a character of the series. In order:
1: The order of the Phoenix
2: The deathly hallows
3: That's a griffon, referencing Buckbeak, the hippogriff from the 3rd book
4: The chamber of secrets
5: Not quite sure about this. A young "dark lord", such as the young version of Voldemort that appears in the 2nd book, perhaps? Or maybe, Kylo Ren being the leader of the First Order could be another reference to the Order of the Phoenix...
6: The goblet of fire
7: The philosoper's stone
8: The half-blood prince
9: The prisoner of Azkaban
Adding onto Teo's answer:
The descriptions of all these pictures are the 7 days of the week as well as "Bonus stuff" and "Long time after". The 7 days correspond to the 7 books in order (Sunday = Philosopher's stone, Monday = Chamber of secrets etc.). This gives us a hint for what pictures 3 and 5 are.
3. Bonus Stuff: This references Fantastic Beasts and Where To Find Them
5. Long time after: This is probably The Cursed Child, written a long time after the original series and by a different author, much like the new Star Wars series.