How far the dog should go will depend on all sorts of things, distance, number of rests and the speed you are going at. Also on the size and fitness of your dog
My dog will regularly do a 12 mile evening ride with and keep up with me all the way, but I am always make sure the route crosses lots of streams she gets well watered and fed etc. She loves it, and also I know from experience that when she has had enough she will just slow down, and make me wait for her. I have found from experience that the 12 mile loop is about her limit before she starts slowing, so thats what I stick with, if I'm going further then I won't take her.
20 miles a day for 5 days, well its possible, but I wouldn't do it myself. 20 miles for the first day prob ok, the second day.. perhaps, but by the third day be prepared to be going at walking speed or carrying said dog.