I don't think putting all the characters in the same class is for the best, actually. This is a pretty big game and having everyone together means waiting on everyone for every class scene. Segmenting it leads to easier to follow and write scenes between smaller amounts of characters, while also leaving room in the class in the event someone joins later.

Plus not having multiple classes kind of defeats the point of having ages range more than a year in the first place. As long as we know who is in what class (maybe a list edited into the first post) then we should be fine.