The 3 schools can just be the sand/desert magics, the illusion stuff for the thieves guild, and the summoning/controlling of the djinn magic.
I have beeen trying to think of unique rules and unique troops besides the ones we know about from the Warmaster Army list. Dervishes perhaps? An infiltrating unit called Street Rats, from the thieves guild? A skirmishing unit of guys with huge scimitars/Kopeshs that wield them by doing summersaults in the air and flinging the weapon over their heads with the momentum of theie summersulting body, effectivly giving them a big strength bonus on the charge almost liek an infantry unit with lances. Fedayeen "one who is ready to sacrifice his life" can be an elite guard.
-Lord: Sultian, Grand Visir, Greater Djinn Summoner, Thieves Guildlord
-Hero: Sheik, Visir, Djinn Summoner, Master Thief, Huckster
-Common: Warriors (spear/scimitar&shield), Ranged (sling&shield/bow), Light Horse Cav (archers or spear)
-Special: Camel Riders, Heavy Horse Cav (w/ 2 handed wpns), lesser djinn (requires a summoner), Fedayeen, Carpet riders (in units like pegusi riders), dervishes, Street Rats
-Rare: Some sort of Artillery, Elephant, Greater Djinn (requires Greater Summoner)
I am doing some reading on different types of Djinn I will post it next