Hey dzodzu,
We are glad to help, and there are indeed plans to improve upon .fbx importing options.
As for the Lightmap UV indexes here is a bit of clarification I pulled from the documentation website. By default, the first set of UVs (index 0) of a static mesh will be used when generating lightmaps for static lighting. This means the same set of coordinates that is used for applying materials to the mesh will also be used for lightmaps. This is quite often not ideal. One reason for this is that the UVs used for generating lightmaps need to be unique, meaning that each face of the mesh must not overlap any other face within the UV space.
The reason for this should be fairly obvious: if the faces share the same UV space, the portion of the lightmap corresponding to that space will be applied to both the faces. This can be great for diffuse and other textures as it allows the texture resolution to be higher for each face. It will result in inaccurate lighting, however. Static Meshes have a property called LightmapCoordinateIndex that allows a specific set of UVs to be used for lightmap generation. By setting this property to point to a set of UVs that are unique and properly set up for lightmaps, Static Meshes can enjoy the best of both worlds: better texture resolution for diffuse textures and accurate lighting from lightmaps.
Here is the link to the documentation for more information about unwrapping and lightmapping in general:
Cheers!