1) Never, never, never pay up for your whole flight training in advance.
2) See 1 above
Training schools like airlines struggle during a recession. Even reputable schools can tank pretty quickly. Pay for your training in tranches, in as small chunks as you can negotiate with the FTO.
Modular training was equally popular as integrated until the mid noughties when the balance tipped in favour of integrated, driven largely by what was at the time being sought by the airlines. The advantage for the airlines is that the training record comes all from one place and generally the airlines are working with a small number of FTOs which allows them to have a certain confidence in the consistency of training and cadet.
Are you better trained by virtue of following one route or another? No is the simple answer - I’ve flown with good/mediocre/not good cadets from modular/integrated/MPL backgrounds. It makes eff all difference.
Modular seemed to become less popular from maybe 2008-2017 but I have definitely noticed more guys from modular backgrounds showing up on the flight deck over the past 2 years or so. I am not sure whether that is due to a change of recruitment strategy or due to a shortage of integrated guys/girls or maybe a bit of both.
Aviation is a fickle industry - I would only go down the remortgage route if I was confident that I could afford the repayments whilst not employed as a pilot. The past 2-3 years have been a good time fo newly qualified pilots. We seem to be entering a consolidation phase with certain airlines going under so the supply of experienced crew will be loosening slightly which is makes the job of the newly qualified, inexperienced job hunter slightly tougher. Beyond the companies which have folded there are no shortage of large companies facing major financial hurdles Flybe/Norwegian/Croatian/Icelandair/WOW/Alitalia and even some previously bulletproof companies in the Middle East.
For ordinary individuals of ordinary means there is no risk free way of getting into the industry - if you are determined to get into the industry you have to take the leap at some stage. Just make sure you have a plan B that doesn’t involve declaring yourself bankrupt.
At 21 you are still plenty young enough to hold off for a few years to save up and even start chipping away at your PPL if you decide to go down the modular route whilst lining up your commercial licence in 2/3 years time.
My route was PPL (took 2 years whilst working a regular day job and squirrelling money away for the next bit of training) -> CPL MEIR -> regional FO -> regional capt -> airbus FO -> airbus capt. It took about 11 years from first flight in a Cessna to the LHS on the bus. I have enjoyed pretty much every bit of it along the way but I would say the most challenging bit and the bit I learned the most from was my first command on a TP.
The employment environment changes from one year to the next so there is a large amount of luck involved along the way in getting to your dream job. You need to be resilient to work through the times when through no fault of your own the opportunities to progress are few and far between. If you doggedly pursue it however you will get there in the end.