Alright, I've been messing around with this for a while and I can't make sense of it. Here's what I have:
* A .OBJ file which is my model, UV unwrapped (...at least I'm pretty sure it's UV unwrapped, I have questions about that but they don't belong here)
* Temporary textures just to test that I can import a model

And here's what I'm trying.
* I'm trying to "submit" (obviously not going to actually submit until I have real textures) a custom Kunkka Weapon, so I select those and input "weapon_rogueblade" in the weapon name box
* I convert my OBJ model to FBX via the Autodesk FBX Converter on this page
* I then make sure the FBX file is named weapon_rogueblade_lod1
* I select the texture

And all I get is this:

Starting compile of weapon_rogueblade...
CTargetMDL::Compile - GetOutputPath failed
WARNING: CTargetZIP::Compile - Target 0 Compile Failed

I've seen mentions of needing to keep to a specific directory structure, namely this one:
Model source content resides in \content\dota\models\items\heroname\itemname\maya\
Compiled model binaries belong in \game\dota\models\items\heroname\itemname\
Material source content resides in \content\dota\materialsrc\models\items\heroname\it emname\
Compiled material binaries and .vmt belong in \content\dota\materialsrc\models\items\heroname\it emname\ and should be named the same as the model
However, which do I use? The Model/Material source content ones? Or is it some other problem? My FBX converter mentioned something about not being able to load or convert the default material in my model file.

(side bonus question: which version of FBX should I be converting to?)

Many thanks if someone can help solve my problem!