They will very likely be fully customizable, especially since some people are way taller than others and the weapon to body ratio needs to fit otherwise you’re carrying a Hammer that is way too big for a normal sized person to carry and cant really use it.
NPCs will all be around the same Size on a per Village basis, though I will start off with a default height between 4 and 8 blocks (1 to 2 meters), since that way a 2m tall person can still crouch a little to get through a 7 block tall Door without having to adjust the buildings to make them not crawl through the doorways. XD