Pikey, I have done all those things: HE lecturer and driving instructor for 11 years. I still do part time lecturing in my local college ( only 4 hours a week though, but the money is good,) and supply teaching . I see every day the stress teachers are under and really feel sorry for them , and anybody that says teachers have long holidays, I say they deserve it. As a supply teacher, I have none of the stress except dealing with the kids in the classroom, but are least I know my day finishes at 3pm no matter what. No preparing, no marking, no assessing, no useless meetings. So I understand your views .
Now for the driving instruction. I would advise you against it as there loads of driving schools out there and building your customer base is not easy. The financial rewards are not what you are made to believe and the expenses can he quite high.
Be prepared to spend between £2000 and £3000 to train as a driving instructor which consists of 3 tests, the last one being the toughest with only 33% pass rate.
Also bear in mind that in 20 year time, there will be no need for driving instructors as cars will drive themselves.
How about doing supply but bear in mind no holiday pay, combined with private lessons?
I am now lucky as I get my monthly pension so work is a financial bonus.
Whatever you decide, think carefully before you take the plunge.