It's all still very much up in the air at the moment, but I don't' see it being any more models than a game of Warhammer.
All the units will be available as a single purchase items including the movement tray/base and will be cheaper then buying them in individual blisters.
It entirely possible I am over estimating the number of units and we may pull it in a little so this is probably 2/3 of an army and not half an army. Of course, it could be bigger if you took all Troopers, or smaller if you took all Highlanders.
Just in case you hadn't clicked, that pic has TWO armies in it, a Britanan and a Orcnar. 1 commander and 5 units each.