Do you have any ideas on what factions there will be ? (Names, NPC's, and so on.) You could go with the Red Anthill and the Black Anthill and the pink anthill, but that doesn't leave room for very much creativity in the factions.
Like Silver Wolf suggested i was thinking of faction with black/red/yellow ants . But within those factions you wont find the same types of ants.
Edit : i just saw your post when posting this one, i'll take a look at those links Grumph, i bet those will be interesting stuff
for example black ants will be small and weak, but fast walking and cheap to recruit/maintain and would act mainly as a swarm when attacking. Of course they would have some strong soldier aswell but weaker than the reds.
red ants could be a little bigger, more aggressive, slow and bulky, thus more expansive to recruit/maintain
and so on
some specialized ants from castles could be those flying ants (behaving like a cavalry)
Leopardo has posted in the french section a database link with lots of free models. I'm gathering models that are licence free and could fit in the mod. i will post their link here if some modelers want to have fun with those later.
edit2 : i've modified the first post to link those models and some more ideas from everyone here, thanks for the faction ideas Grumph, i've added the black garden ant and green ants to your proposal