Those sprites are looking good - and I like the proliferation of mounted units: mobility on the battlefield should be a major advantage of an Arabian faction.
If you're setting up al-Nadim against Hinnom, you could play off of the tangle of myths surrounding
Sulayman/Solomon, in which he tamed, captured or enslaved the jinns (or, according to
Christian Goetic sources, the demons of hell) - that could make for an interesting hero, at least
And if you decide to do a MA version, you could go with a "Great Caliphate" theme - think of something a little like EA Aeroscaphle and MA Tien Chi: that would play off of the scholars, poets and alchemists of the 1st & 2nd Caliphates and the anti-Caliphate (Moorish Spain) - these historical empires had their heyday during Europe's "Dark Ages."
I don't have much advice regarding Arabic mythology - the previous paragraph was drawn from what I remember from some of my undergraduate history courses.
Another thought: it might be interesting to imagine them as caught between Abyssia (which incorporates some Middle-Eastern tropes) and Hinnom. If you don't want to do a MA version of al-Nadim, that's more than enough explanation.
Sorry, that's probably too many suggestions too quickly. I'm like that when I get going.
Short version of this post: Neat!
I can't wait to see more.