Everything will be imported into your project when loading a family. If the Family already exists you will get a message stating "You are trying to load the family xxx, which already exists in the project. What do you want to do. Your choices are 1. Overwrite the existing version or 2. Overwrite the existing version and its parameters.
As for loading same names, materials, line types, etc. typically everything in your project will take priority. Revit will see the incoming item and tell you that its already exists and in some cases it will re-label to avoid confusion. However, it depends on the item and what'how you are loading it.
Hope this helps and thanks for posting.