In the interest of hopefully providing some info, but at the risk of possibly stating one or two things not entirely correctly, I offer the following, with hopeful corrections as needed from the dev side to come.
OBJ is the primary object input format for TG2, so at the very most TG is limited to what OBJs can represent. Most of the time you will want to assume the simplest version of the format, e.g. triangulate everything, no fancy model representations (e.g. NURBS, although these would be turned into geometry on OBJ export normally anyway).
TG2 needs a validly formatted MTL which refers to the appropriate texture maps. TG2 does not currently respect material *properties*, for the most part, only texture map references and UV mapping. So if you want e.g. a shiny texture area, you would create it with the basic texture map and UV in your modeler, then just set it up as specular with a TG2 shader.
I don't think repeating textures are respected either, so ideally you would have a single texture that covers every UV mapped area you need to cover. An alternative could be to use TG's built-in tiling for image maps, but I'm not entirely certain this will have the same results (or at least that the results would be easily duplicatable) as your modeling/texturing app.
I hope that helps a bit.
- Oshyan
