Most likely.
You could also enter in anytime after or what not, but you don't seem to have a champion quite yet. I'd suggest asking one of us to make one :P.
I'm almost done with the Blood Champ, he'll be posted later this evening.

There's quite a lot of plot I didn't throw in.
Like the Godess of Souls and Shadows. They are there, but haven't quite acted yet in reference to the major events.
Valios taking the dark path may or may not be crucial but the Darius being chosen by the God of Magic is something of note given that Hawke was another candidate. Hawke then might be chosen as the champion of Secrets which then would give him insights into plot :P