In order to be a dentist you need to have a certain amount of maturity. I think that will be the biggest barrier to you in reaching your goals.
To answer your questions:
Not all implant cases are the same. Some are very straight-forward with good anatomy and everything ideal. Others can be very complicated. Some dental students place implants in dental school, and all will need a significant amount of continuing education possibly including GPR/AEGD to place implants and even then, they should select their cases carefully and refer many cases to a surgeon. It's the same thing with orthodontics. Some cases are straight-forward, others are not. A well-trained GP should be able to do orthodontics in his/her office.
No one will do a residency in orthodontics and oral surgery and then practice as a GP. It makes no economic sense because of the cost of the training, and you will not get any referrals from other GP's. You will not have enough ortho and surgical cases from your general practice pool to justify your training and even if you did, you only have 24 hours in a day to do general dentistry, ortho, and surgery. If you really want to practice with the broadest scope possible a 2-year AEGD or GPR would be a good idea.
Dentistry is a great field. Generally you will not make 500,000 a year no matter what type of specialized procedures you're doing but you won't worry about money and you can make it into the upper middle class. It can also be extremely fulfilling if you're doing quality work.