Mounted scout is good idea (though it won't use its MV 3 at enemy territory, of course).
On water mages, etc.: they will probably appear at MA/LA, as Berberian Corsairs were famous enough and terrorized Mediterranean up till 19th century!
At MA/LA nomads must remain (they did, after all!), but become no longer mainstay troops. I would make basic nomads just slightly stronger than militia, and accordingly cheaper than indeps infantry/cavalry, to make them massable. I don't think that to make human troops with higher stats "just because" is such a great idea.

On eunuchs - certainly not in early era; also, we already have assassins in MA (& yes, I know that sacred assassin should get a bless or his sacred status is wasted

), while using him as spy is just about as ridiculous as is the case of FFA (who won't be able to notice such a "spy"?!

). If we could make them useful in some other way, such as reducing unrest, or research without magic, it would be much better.

Courtesans, on the other hand... are completely out of question

- there was no such tradition in the Middle East! Wife of harem could hold much actual power, but she would need to have MV 0

& have some beneficial effect in friendly territory (healing, for example). Female thieves were also known, but they were not courtesans - just Thieves of Bagdad who happened to be female.

And regarding thieves - in Persian region at least they were often hired by powers that be to provide policework - interesting twist for MA, isn't it?
Another probability for early age would be a travelling poet - these were considered somewhat holy and able to influence geniekind.. Here we also HAVE a possibility for national spy

- though only in EA (by MA some kind of Thief of Bagdad should replace them in this respect).
And if somebody wants to know what I think about double-scimitar wielders...

well, I included some in my own mod..

they just not in style of early Arabs (apprentices of Alamut is something else again, of course!

)