You only need a PPL to instruct however the instructing you can do with it is very limited, realistically you need a CPL with Instructor rating. Think Par Avionics in Tasmania used to do flight training. At your age there is no problems with a career instructing. As for schools don’t pay up front and visit as many as possible, generally I find smaller schools are good as you get more one on one time (and hopefully if you go all the way through you may end up with an instructing job at the end). If time and money isn’t a problem go for trial flights at a few schools and see what feels the best fit for you and ask lots of questions.