Your ECT year will be 60-70 hour weeks min for sure.
But once you have done it, a lot more options will be open to you. You don't have to stick with being a mainstream class teacher based at a school.
I think most people who have the financial security you describe have had to do at least a few years without the work life balance you would like. You need to establish yourself first then you can start to be a bit picker over roles that suit your lifestyle.
It takes that extra level of effort to develop the skill set to be able to be able to move forward in my opinio, it's not just a case of 'doing your time', to become highly skilled enough for higher paid roles etc you need to spend a few years on a steep learning curve.
I did mainstream class teaching for 3 years, moved into specialised SEND teaching roles, Senco (with a FT Class) but last year, 9 years after qualifying I started working as a specialised teacher in the LA'S Ed Psych team, which is probably 40-50 hours pw with flexitime and about 50% the time I work from home, I feel like I've hit a good level of work life balance now.
I was only in a position to afford the lifestyle you describe from about M4 upwards. Being a homeowner and having just a basic level of financial security, rightly or wrongly, takes a fair bit of effort these days.
You sound a bit nervous about your ECT year. You have passed your teacher training, what makes you think you would struggle? And you now have extra experience from supply.
Even if you change direction, you will still need to spend most of your 20s working much more than 40 hours a week to achieve the goals you described. I work closely with social workers, health professionals etc and its exactly the same with them.
Good luck if you go for an ECT role xx