In answer to the allies question. No you cannot choose allies, besides making it more complex for me to administrate it could potentially allow you to enter 4 different codex entries, which defeats the objective. If you want to use allies they will count as your second army choice.
Count as models, well that may be different. If it is actually representing something from the codex then thats fine, but if I think your not sticking to the rules I will let you know.
awe spoilsport ;) how are we meant to torment you if you won't let us choose irritatingly fiddly model/unit combos?