@Valiance… first:
Second: It depends on what you want to mod. Exchanging the look of existing items or models will be rather easy and you do not need to “code” too much. No real “tampering” with the engine. If you want to add something basic, like a new weapon, you will be able to copy the data for an existing item and adjust it. The more complex your project becomes, the more you will need to work with Lua (and JS / HTML). However, you are not really going to work on the level of Stonehearth’s engine (which is not accessible and coded in C++).
On animations you want to take a look into Qubicle Constructor (see attached post) to create models. As an animation tool I prefer Blender myself.