I'd use some PavArbs, Light Cavs (so Hobilars and probably a LOT of mercenary HA). To fight with Islamic factions in the desert I very often use hordes of mercenary muslim troops. I think that PavArbs should form the core of such forces. It makes no sense to get any knights or any other heavy cavs, just some good spear infantry as a backup for all those missile units, and I think that plus some decent general (at this point you must have many) and i think that'd do.

Regards,
EC