I have not done super long distances but my experience from 1-2 weeks is as follows.
Touring is different to your day rides at home. You have all day to cycle. You cycle at a leisurely pace, take regular rest, you need to admire the scene and take photos, stop at various restaurants to taste local delicacies. I would say moving average of 12-14 miles and total average of 10 miles a hour is a reasonable speed to aim at.
Vary the distance according to the terrain. If the terrain is flat and easy, do 60 miles. On more difficult, hilly ones, do 40 miles.
Have a rest day after every 7 days of riding. You can not keep riding everyday.
Remember, you get fitter as you ride.
Good luck.