Well the villagers have different profession textures that go over their skins in the game, such as farmer or librarian. I am altering the profession uniforms to fit with my custom villagers.

As for levels, when you trade with a villager they level up, and there is actually an indicator on their belt to show what level they are, but I always forget this as it is super hard to see. I am adding a necklace to them because I feel it will be super obvious to me when looking at them, right in my face. Instead what I usually do is run around talking to the 3 different blacksmiths trying to find my high lvl one lol.