All of my models will come with two choices; 1K and 3K. Options to have 6K will be forthcoming. 

I would have but the packed model would have exceeded 60Mbs. Instead, I have the Blend file and textures contained in separate entities. This way the Blend file is below 20Mbs and the textures are in their own folder. 

Yes, you can APPEND the Blend file. Do exactly as you would do when appending. You will find 2 different model quality types; a 1K and a 3K. The textures will follow suit. 

Each model has an "EMPTY" assigned to it. Simply move the EMPTY and the rest of the model will follow. I did this to simplify manageability. 

Sometimes materials like to run away from their models. This can be remedied quickly. All you have to do is go into the material panel, open up the Shade Editor, and relink each textured image to the corresponding folder. That will relink the texture with no UV editing required.