This question always comes up.
It is madness to plan to be a career light aircraft instructor. You are lucky if you can get 20k in a year and that is below the national average and the mean wages in the UK.
Yet you have to find 60-100k of your own cash to get the ratings. You'll never earn it back.
I am biased - I run a microlight school in Scotland - but I think one would do much better buying a microlight like a Eurostar or C42 Ikarus (at 50k) and getting a microlight instructor's rating (about 5k) - on yourbasic PPL.
I am, in fact, sponsoring a PPL through this route to provide an instructor for me at Strathaven.
If you can get 20k a year doing a job you really really love, and without a massive debt burden, then you have prospects. If, every time the the credit card bill, the personal loan statement and the bank statements comes in you feel tempted by a move to airlines, you are building up stress for yourself.
Other routes are getting a 30k a year job as a train driver - 4 days on, 4 off - and being a PFA coach on your days off. You won't make any money from your flying, but you'll get the fun of sharing your knowledge with others.
If you want to teach, and want to make a living, the last course you should go down as a basic PPL is FI (SSEA), in my view.