My advice is you may need a CELTA to get the better jobs, work in the middle east (where the money is) or to obtain a visa in some places like Vietnam, Indonesia etc.
Think of the CELTA as an expensive, work intensive way of opening doors for yourself. Once you've got it take what you want from it and forget the rest. It's like driving a car - During the driving course you have to drive like an absolute spaz to conform to the standards laid out by the instructors. After you pass you can drive whatever way suits you best.
Teaching teenagers has to be easier and more fun that kids, surely? Give them some grammar, let them practice and have the aim being that by the end of the class they can add their existing vocab to the formation you've taught. Make sure you work towards the goal of letting them do something interesting with what you've taught them at the end of the class. You're not going to set the world alight playing videos every week or passing them on exams that may be beyond them.