At your age, you might find that you could lose some of your existing native hair following the transplant. From the pictures, I see a low crown balding area which suggests that you might develop an advanced balding pattern in the long term. The use of the drug finasteride reduces this risk, but balding in men is progressive. Ask your doctor where your balding pattern might end up. Find out what your donor density is, so that some calculations of your reserve donor hair can be made now, before you start your transplants. Keep the hair transplants to the frontal area only, because if it goes into the crown, then you will be caught in a conundrum with patches of hair transplants in the front and in the crown will leaving you not normal looking. These steps will be the best approach to minimizing the risk of getting into multiple hair transplant surgeries as you lose more hair, which you should expect to happen. Your goal should be that just a single surgery will stand on its own and that is why I am suggesting that you only transplant the frontal area at this time.