The first question I can answer in some greater depth. What we've done here is building the army tradition trees in a historically progressive way. One adopted practice leads up to the next, and so on. There's an emphasis on common practices adopted by certain factions, which were historically put in use. These make up the bulk of the army traditions. In several cases, important historical events are baked into the trees as situations where specific strategies were adopted to solve problems, either of a logistical kind or directly involving combat. These are of course subtle, there's no direct mention of said events. Carthage's Truceless War, for instance, is one branch of their tree where you can adopt traditions based on lessons learnt from that conflict, such as mercenary loyalty and upkeep. There's part of Parthia's traditions revolving around Carrhae (see spoiler below). The Greeks have some legacies and ambitions from the conquests of Alexander, with mutual cultural exchange being one of the key words.
Typically, an army traditions tree consists of two main branches, a logistical and martial/disciplinary one. These converge into some top tier traditions which require both branches to be unlocked, that would realistically require both aspects to be mastered. Then there are some additional side-branches, such as garrison duty for the Romans. Religious practices, in particular of the Hellenistic factions, is another area that we've put some emphasis on. See spoiler for previews.