Yes sounds like a pyramide in the end, recruiting more and more students an promising them a chance of instructing if they invest, however there is not a bottomless pit of fools that will spend £75.000 on the their pilot education.
What about insurance, accounting, maintenance, and you would need to have a chief pilot/instructor that was CAA approved.
Now if I would invest £75.000 in a business, I would want to have some profit of that. The "new aircraft" at £200 - £300.000, would not have anything close to this NEW value after 6 months or more. With students bashing about on these aircrafts they would be pretty well used within a few years. So your initial company value/investment would be less then what you invested, the only way to increase the value would be to get more students paying for their courses, so your turnover increased.
There are people today with shares in airplanes, from £5000 to £20.000, they struggle to sell them on when they want out. How easy do you think it would be to sell on a £75.000 pilot course, when you have no name or reputation?
Why would anyone risk so much money, when you can NOT be certain of anything. If you do not attract enough students then the concept fails, if you attract to many students - it becomes a pyramide - where the bottom chain will loose because there will not be sufficient supply for you to be able to keep your promises, unless you are prepared to have xxxxx number of instructors! You will need more than 1 airplane though! For that amount of instructors and students!