Sorry, I don’t really know that much about modding Stonehearth - did my very first look at working with models (and mods) in Stonehearth (and any game for that matter) yesterday.
However, I’d say simply browse the models found in the original pack and make your decision from there.
It’s your mod and your call how much you want/need in it, right? 
I think what you should focus on first is:
- models that represent the parts of your Hearthlings/Lizards
- models that represent the way of life of your Lizards (stone beds, stone tables if you need new ones, stone chairs if you need new ones, later on maybe even bluprints for houses?)
- ways to reach the items already existing in Stonehearth (e.g., to be able to promote to Carpenter and get access to all exisitng Carpenter items?)
- Different clothes for different jobs/profession (Worker, Mason, Farmer, etc)
These would be my guesses/suggestions at least 