An idea could be to also implement some units that are unique to several civs. Some excamples:
Varangian Guard - UU for Sweden, Norse (not Denmark-Norway, as they were way later), Kiev-Rus, Byzantines and Saxons. Basically varangians were norsemen who went into service as mercanaries for mainly the Saxons, Byzantines and Kiev-Rus.
Frankish Knight? - HRE and France
Italian Militia - Venice and Papals... you should find a way to implement Genoa as a civ too.
Berber Cavalry - Abbasids and Umayids
Hussar - Poland and Hungary... I know these were a bit later, but anyway...
Some extra UU proposals:
Norse: Longboat, Viking (not 'Berserker' or 'Viking Raider'... viking was originally a noun for Sailor and later became a verb for 'to go pillage' or 'to plunder' or 'to go pirate'), Birkebeiner
Sweden: Goth, Longboat, Leidangr
HRE: Teutonic Knight, Landsknecht
Venice: Galleas
Saxons: Huscarl, Fyrd
Byzantines: Dromon
"The Spanish Kingdom": Jinites, Almogavers
You might have added a couple of these already, and I have to admit that I have not played your mod that much, but I have tried it for a short while, and I like it. I hope you like these ideas too