Yeah, since I made that comment I started making some progress towards some mods of my own, but I get stuck when importing them into Studio, as they just don't show up... is a UV map necessary if the mesh data already has textures applied to it?
Depends on what you are making.
Not showing up can be lots of things.
Make sure to apply the scale, position, rotation and all that stuff to the object before importing it into S4S.
uv maps, not so sure. iirc 1 uv map is for texturing and another one is for lightmap baking in realtime, so its reccomended to have the second one but, most of my ports work with just one just fine.
I would prolly be able to help out a bit more if i could actually see the error/issue, would be easier this way