You raise good questions, especially for someone considering striking out on their own.
Personally I'm laser focused on this question: "How do I match what I could earn in salary as a software engineer?" Beyond that - I can figure it out on my own. Until then - I'm burning savings and need to figure it out.
As far as I can tell, the safest fastest way to get from A (unemployed and without income) to B ("engineer salary") is as follows, assuming "engineer salary" is 150k/year.
1. Have enough savings to live for 1 year with $0 income and another year with reduced income - say, 50k/year. Having 40k on top of that in savings: half of that to get you started, half to buy businesses in the future and/or to buy services to do that then.
2. Buy an ad supported online business on Flippa. Budget: 20k. This can be for one or multiple businesses, though multiple is probably better for quicker growth & profit potential. (It doesn't have to be Flippa btw, but that's 'good enough' for our purposes).
3. Assume no income in year 1. In this year you add pages to your site(s) and continuously improve them, using Google search analytics to confirm what you're doing is working. Your traffic should be increasing.
4. Assume 50k/year income in year 2. This is either through ad revenue or selling one of those sites you bought (probably the latter). Continue doing what you did in year 1, but better.
5. By year 3 you've hit your goal. By year 4 you've exceeded it. Every year after that, you can expect your income to substantially grow, for at least the following 3 years.