currently, I'm thinking of the following types
a) arab type light horse that would be used throughout asia and north africa (representing the ancestor of the similar marwari horse in India and berber horse in africa) roughly trying to recreate the turkoman here.
b) a heavy nisean horse that would be used by elite cavalry units of eastern factions and asiatic diadochi factions like seleucids. could be used by cataphracts too but those are in reality hidden under the armour so the model doesn't matter much, only size does.
c) medium thessalian/thracian/greek horse primarily used by elite units like hetairoi and general's bodyguard in greece and balkans
d) medium andalusian horse for elite units of rome and spain
e) a light european horse, still undecided on what to base it on
f) a mongol pony type horse for the steppe tribes.