The most important thing for the next 5-10 years to me is a) be happy b) provide for my family (I do have two kids and a stable marriage). All my jobs until now were very good, but I was hardly happy at them. I worked at big, big name companies in tech and also in one start-up, albeit not as partner.

Maybe you should start out with part-time 'regular' work, and do your start-up stuff on the side, then as you make more money on the side you can build down your 'regular' work. That way you get to do it without taking the plunge in an all-or-nothing fashion.

What's the best way to find that kind of work?

Anything will do, really the only requirement is that you don't have to be there all the time, so this is more geared towards the kind of job where people can be replaced on short notice without interrupting the workflow.

Think retail, that sort of thing. All you need is for it to cover the basic expenses and to leave your head free so you can think about stuff while doing the work. Then when you get home you're not too mentally tired to do some 'real' work for a bit, and on your 'off' days you can implement the stuff that you've been thinking about / working on on a slightly larger scale.

When I was 17 or so I worked in the mail room of a bank while at the same time working hard on becoming a professional computer programmer. If the work had been more demanding mentally that would have been a lot harder.