I agree with DL that variety and enough calories are important for juicing for long time. It is very healing and your body will not go in Ketosis, but that is not the goal when you eat. juicing is used in the Gerson protocol. Although Dr. Gerson did not allow any fat intake, whatever fat was in the fruits and vegetables that's what you got. Avocado is a good choice and some seeds too, but I would not do oils in this case.
Smoothies are a good idea.
To me one more important part is food combining. So be careful of what you put in your juices.
You will starve if you just drink only orange juice everyday. As in all fasting and dieting phases we should always listen to our body and know when to stop.