I was doing some research myself over the past few weeks (was looking to tweak a few units from my old XC3), So at least a few points can come in useful on here: mostly archer stuff.
Germans:
The area typically had little in the way of iron, and as such used more clubs and maces, instead of swords or, more prominent in the RTW engine; axes. Of course they were around, but not too common, so maybe the sheer number of axe units might be toned down a little. This wasn't by chance: A culture lacking in iron had little in the way of iron armour, and so focused on armour piercing weapons to try and even the score against armoured opposition. I believe the closest large resource of iron was sweden, hence the big axemen (feorldmenn, eorldmenn, huskarls) of saxons ,danes, and norse from around 4th Century AD onwards. Maybe putting the 2handed axemen as some kind of AOR unit from skandza or jutland might work out better, or possible switching the "2 handed axemen" and "berserker" roles in game, with zerkers being toned down a little and made standard in unit numbers.
Romans:
Had little in the way of effective heavy cavalry (im seeing the "preatorian cavalry" here). Most of the early republic used spain to aquire cavalry, so as mentioned in another post, maybe more spanish AOR cavalry.
Archer auxiiaries were almost solely AOR (numidians, cretians, syrians), not recruitable everywhere. Though roamans did know of the composite bow, i cant recall from what time frame this was.
A little under-represnted archer wise. Archery was bigger in the eastern diadochi's than the homeland. Reports mention compostie bows from way before RTW's timeframe (as well as a vague refernce to a bow "of composite design" actually found in Tutankhamens tomb). Along with the scyian/cimmerian rampages across syrai and the levant of around 6th C BC means they would most certainly of had composites.
Nubians also had a longbow, similar to the indian, as well as the Ethoipians, the latter of the two is backed by Herodotus; mentioning 4 cubits long at least, making something near 6 foot??? (no 69):
http://www.sacred-texts.com/cla/hh/hh7060.htm