Red Harvest, what you suggest sounds good but I suspect units will be built in the usual way - piecemeal.

Actually, it may work ok as it is - for example, from the demo, it looks like the hastati, principes and triari are nicely differentiated. The hastati are classified as "light" and as such seem to have an edge against elephants. The principes are a little bit better attack than the hastati, while the triari are worse at attacking but are better at holding off cav.

When we get to the Marian period, presumably spear armed auxiliaries of some sort will be required to replace the triari.