For static models I just put them in a folder within the entitybank folder.
You'll need at least three things at the moment:
1. a model in X file format, e.g. "myHouse.x"
2. a single texture file, e.g. "myHouse_D.dds"
3. an fpe file, e.g. "myHouse.fpe".
(While other possibilities might work, the above should be enough to get you started.)
Ideally you should also have a thumbnail image for your object, e.g. "myHouse.bmp" - just create an image similar to one of the existing ones. However, you don't need this image for things to work - it does make your media look more professional though.
The safest model vertex format at the moment has just XYZ position, NORMALS and one set of texture coordinates. Other formats might work but nothing is settled yet.
Your fpe file should be similar to the ones used for the stock entities, just copy one, then make the obvious changes to the file name and the relevant references inside the file.