This has been a great read! My story is less interesting than the ones above, but I'll share. I basically worked for the same engineering company for 19 years after college, being a big part of the company expanding more into structural work. That company was eventually acquired by a larger one a couple years before I left, as they wanted to offer structural engineering as one of their services.
Aside from my engineering job, over those years I bought and renovated a duplex and did occasional side work as a carpenter. The duplex, despite being bought at exactly the wrong time (in 2006) has finally paid off, giving me enough passive income to make starting my own company a much lower risk than it would have otherwise been. The carpentry and construction work that I've done both for myself and for others has made me a better structural engineer as I'm always thinking about how I would construct one of my structural designs.
Upon leaving my employer, I decided that I would take the next year and a half off to specifically study structural engineering and write software. This also happened to coincide with an 18 month non-compete I had with my former employer, so the timeframe seemed to make sense. I saved enough before I quit that I knew I'd be ok financially, especially considering the passive rental from my duplex as well as another property that I manage for a friend.
I've only been in business for 5 days now, so I don't exactly have a ton of perspective, but I think this is going to be good. This is a great profession for starting your own business. The start-up costs are extremely low if you'll be working out of your home. In case anybody's curious, I'm estimating about 10-12k for the first year, but I think somebody could probably be operational for 5-6k. Some things that I paid more for make sense to me, like not using the cheapest insurance company.
When I was working for somebody else my duties included: discussing projects directly with clients, determining engineering fees, writing agreements, receiving signed agreements, designing and drafting plans, stamping plans, and providing construction services. Now that I work for myself, there isn't much additional stuff to do, mostly just accounting/billing and some minimal administrative tasks. One huge benefit for me is not being excessively pestered about meeting some arbitrary utilization ratio, or having to deal with the fact I had 1 hour of overtime which wasn't approved.
I say when you're ready OP, go for it. Put yourself in a good position financially beforehand so it's as low risk as possible. Ideally, you don't ever want to be in a position where your back is against the wall and you're forced to take on a bad project or client that you'd otherwise run from.