Hi
1. To make a bone (or multiple bones) you have to create an armature first. Then go into edit mode and rename the bone to something else you want. In edit mode you can also add more bones.
2. You have to separate the bits from the mesh from the other parts. For more information, please refer to the following threads
1 2.
3. Depends on what you are making. If you make a mesh with recolourable and non-recolourable bits then you must make those as separate objects, otherwise there might be some unwanted effects. Also, if you are planning to make something that relies on hiding/showing parts of the model, then they must be exported as separate meshes (with nodes).
4. Yes, you should refer to the default weapons/items. They are made with recolourable textures and their colours are defined in the script.