Can i suggest some ideas, being an arab myself i find it weird the game is lacking a distinct arabic faction (its a great game nonetheless), and i find this mod really interesting.
I'll list 3 ages to reflect some history, Tribal (Early), Imperial/Caliphate (Middle), and Taifa (Late).
For the Early Age(Tribal Age) the Al Murrah are a tribal confederation, with units more or less exclusively arab (reflecting on actual history)
Tribal Warband:basic infantry unit armed with swords, leather armor, javelins and large wooden shields.
Shiekh: Though i like your description, i'd still say sheikhs vary, some of them are warlike and like to lead from the frontlines and some hang in the back preferring to not fight.
Ansari: Remain unchanged, good light cavalry.
Camel Riders: unchanged, your description fits.
For the Imperial/Caliphate age, the Al Murrah start augmenting their army with non-arab, and slave troops as mentioned above Dervish (mountain people, primarly kurds) and Mameluke (turkish slave troops), though if you wouldn't mind i have better sacred name versions:
Sacred version of the Dervish could be the Serwan Peshmerga (Death Soldier) they reach a point where they totally cast away any fears they have and are pretty much crazy naked berserkers.
Sacred version of Mamelukes can be Fursan Al Halqa (Knights of the Ring, literally), a better armored version of their predecessor and improved generally.
Jund: Better armed armored version of tribal warbands.
Cataphracts: Heavily armored riders, though not to be confused with byzantine or sassanid ones, the arabian ones had leather lamellar armor mostly and leather barding.
To reflect the Caliphates centralisation, units will be lead by Qaed(Captain) which is an upgraded sheikh.
For the last age the Taifa, the Al Murrah have degenerated and become squabbling kingdoms of princes (Amir) and governors (Wali) without a central leader, they rely mostly on mercenaries and primarily non-native troops. Mamelukes and Dervish units will be present, aswell as:
Askari: drilled and organised heavy infantry, they use spears, metallic shields and chainmail or iron lamellar.
Lancer: armored with chainmail, lance and adarga shield (heart shaped shield)
Thats about it for now, these are just some ideas i have gathered for this mod to be used or not at all, i'm pretty new at the game and i have no idea how i could balance this all, so i'll leave it for the mod author to assign whatever he sees fit. If you like this, i'll provide more information with mythological units such as Djinns, Selbouhs, Ghuls, Ifreet etcetera and some wacky stuff like flying carpets and dancing ropes in my next post
i'm not sure if its possible to fit these in the game though.
Hope you like it