As to the best of my knowledge:

1) Model files have one group only.

2) Bones indexes start with the root bone, so there should be no forward references. I'm not sure if the SDK sorts the indexes, but I believe it doesn't.

3) The second UV set can be found with TriangleSkin(index,1) - if index is nonzero, the mesh has a second UV set.

4) I'll pass the buffer save request to Wladimir. He's occupied with another project at the moment, but when overworking the SDK the next time, this can be implemented.