Considering this game is a bandai tie in with Monster Arts, don't expect any monster that hasn't already been made into a monster arts yet.
So if all monster-arts monsters get put in the game, you'd have a pretty good roster-- but I highly doubt all monster arts monsters will make i in there. My guess is the game will have 3-4 playable Godzillas and other godzilla-like monsters (like Kiryu, mechagodzilla2, and so on).
So probably Heisei Godzilla, Godzilla2000, Legendary Godzilla, and Godzilla64 will probably be the four Godzillas we'll get.
He is 350ft Tall people, those things on his neck ARE gills, and the Brazil photo is part of the final advertising design-- Deal with it.