Well, if you choose nomadism, after constructing "Elite Herds" and after that "Warlords Horse Herds" and "Royal Horse Herds", you should be able to recruit most of the Pahlavan Cataphracts and Horse Archers, you can also construct "High King Herds" for another type of cataphract. And by constructing Settled Community (in some settlements) you can recruit Shivatir-i Marda foot archers and Gund-i Nizagan spearmen. Choosing nomadism is the best bet for not-important cities and specially for the cities which are in steppe lands.
But if you choose Pastoralism, after constructing these buidings (note that building them in order is necessary):
Military Occupiation
Migration
Pastoralism
Nomad Market ===> Large Nomad Market
Settled Community
Elite Herds ===> Warlord's Horse Herds
Reformed Pastoralism
Advanced Settlement
Settled Aristocracy
You should be able to construct Parthian Reformed Government, which will allow you to recruit regional Pahlavan units, such as Thanvare Payadag (Parthian foot archers), Gund-i Palta (Parthian Skirmishers), Gund-i Nizagan, Parthian Archer-Spearmen along with most of the Parthian cataphracts and horse archers and in the top of them, Grivpanvar, the Elite Pahlavan Cataphract which will be available after the marian reform AFAIK. It's better to choose this type of settlement for your important cities.
Parthian Reformed Government also allows you to build the main buldings of Pahlava which you can't in nomadism, such as walls, higher level of agriculture, roads, granaries, ports and many more buildings.
Hope this helps.
