So more details:
For now: you apply the textures to the materials in your 3D suite of choose. Just to keep processes simpler, make sure to the textures are relative to your model as I described earlier
For example with relative paths
/folder/Model.fbx
Then you got texture s at
/folder/textures/file.PNG
So that everything when you upload is relative to the model.
However If you happen to have your textures -all-over-the-place, then you
You can also use the interface client it self to bundle models and texture to this sort of directory.

And then this will fetch the model and all the textures referenced in the model into a folder structure. It creates and fst file which overrides your fbx file to use the relative file system. (as far as I know)

Dunno why it creates the joint info thought as those are not present in the file
Anyway, uploading the fst file and the folder it creates to your server, and then using the fst file works. If you didnt do the packaging then remember to upload all the files related to the model in the same relative structure.
Hopefully that helps 