First off, this mod looks excellent, I was sad when AOH died, but it seems this mod is continuing and progressing far better.
Now on topic, we all know that Sparta suffered from the problem of a small population, and a large number of helots.
Now the problem I foresee arises from RTW's recruitment. The faction preview of Sparta shows regular Spartans as well as helot hoplites and others. These troops, and others, were only called upon in times of need, when the Spartans number were not enough. However, if the city pop of Sparta gets to a point where it can no longer recruit, then the idea of helots filling up the ranks is void since no more troops can be recruited.
To get around this I suggest that the only troops able to be raised in Sparta should be Spartan hoplites (And royal guard etc) only. All other troops, such as light infantry and helots should be recruited from the mercenary pool. This way, if Sparta's population is too low to recruit troops, it will force the player to recruit helots from the merc pool, thus representing the historical accuracy I described earlier.
This idea could extend further to all cities. For example in Athens, most units were recruited from the citizen class showing that they had a well-rounded army supplied from its citizens, and therefore the need for mercs would be less. In Carthage however, the only citizens that fought were the poeni in emergencies, and the sacred band. Therefore the merc pool for these Carthage should have all the other units it used, such as Scutarii from Spain, and Libyan Spearmen. To place the emphasis on this mercenary army, poeni and sacred band should be extremely expensive, makin git more logical to recruit from the merc pool. Since the army is merc, the population of Carthage would remain high, meaning taxes would be high, meaning more money to pay for the mercs.
As you can see, the idea I am trying to get across is how recruitment from cities and the merc pool can be balanced on a per city level, in order to represent how the various cities recruited historically.