furthermore maybe a kind of lather could be created for specific units like to hire a classical hoplite one would have to disband/upgrade an hoploi unit with x amount of chevrons

to get peztharoi one would have to disband/upgrade a unit of levypikeman and for argaspydes (or whatever their name) disband/upgrade a unit of pheztaroi

hastati ==> princeps ==> triari

both historical correct and great for roleplaying imho
That's not really how it works...

The difference between Levy Hoplites and regular hoplites is equipment/wealth, basically. Same with the phalanxes you mentioned, as well as the Roman troops, though experience would apply more in that case.