Easy Playable Creature Creation

I want a method/building style that allows me to create a good amount of playable creature characters easily.
I created an amazing GUI system for character selection, but the models I originally intended to use ended up being too complex and I couldn’t find a way to turn them into characters.
I’ve tried creating brick built models, but I can’t find a good way to create rigs so they can actually be played as characters.

Models I originally intended to use: