I already stated there will be both Foederati and a few 2*2 units like scorpio. But, these will be HIGHLY dependent on which path you choose. Foederati will have preset gear to decrease the micro, and they are relatively easy to replace. There will be a few kinds of course, and you will be able to upgrade them when you get better tech. But, Foederati sub-path is a swarming one.
Tanks and drones won't be here. Romans could develop steam tech if they had blast furnace, and we avoided the whole Dark Ages thing, but tanks, same as ironclads, require way more iron than Romans could reasonably mine and process. Keep in mind, your craft will weight more than even a balloon can lift, and WILL need repair very often. I don't think anyone would enjoy waiting 2-7 months for repair.
Drones would require either AI or radio control, and electricity, I don't think I need to go deeper.
Animals, I don't know. When I think of X-Com animals, I remember Piratez, and the brave cats and dogs trying to kill flaming aliens and burning alive. Maybe as very early unit, I don't know.