How hard is it to make a graphic unit mod for AOE2DE?

I want to have a mod for DE where the emblem(s) of the civilisations would replace the other marks on the Cavalier/Paladin shields, galley/galleon sails, pikemen, and more.

I would also like to use the heavy pikeman and Eastern swordsman skins for Cumans, Indians, Mongols, Persians, Saracens, Tatars, Turks. I will have to modify them a little for each civ, and find a way to make decent historical models for Chinese, Japanese, South-Eaat Asian, and American civs.

Do you guys have any ideas on how to do it, and where to start?