How to make model for character customization.

Hello there.

I have request of make character for game. This character should be customizable. Problem is in that I can’t use shape keys ( i seen that way of make character for game) and model have to be one piece.
I heard that in maya is easier I was asked if blender can:
-make mesh groups
-can export mesh groups saparantly with its own weight painting and attachment to skeleton

I heard that in maya it can mesh groups be hidden and unhidden when it’s wanted. It would be nice to make it in blender but in way that it can be still hidden and unhidden in game engine too.
It can be done by cutting it into saparate meshes like head, torso, legs. But it don’t want to fit perfectly after paranting to mesh and no matter how I play with weight paiting there are still holes.
If idea with few objects would be ok I would be fine with unwrapping and texturing but with one object but ton’s of groups I can’t imagine how to unwrap it and texture it.

I hope you understand what I have in mind