Welcome to the indie game.
The first realization is that despite you have 12+ yrs of experience it's only functioning as a tiny cog in a larger operation whereby most of the work was out of sight and out of mind for you.
Everything from advertising to marketing to sales to business management to account management to billing, to project management, to development to deployment to support now falls on your shoulder.
And guess what, engineering for most businesses are the least expensive line item.
You probably want to match your last salary, so say you were making $150k/yr then really you have to find $200k for 2000 billable hours. That's $100/hr.
In terms of contractor rates that's pushing towards the top end of the market when most devs are hovering around the $25 to $60/hr range.
So really, to make that $100/hr billable rate you will have chase a lot to deliver that kind of value.
Most small-medium sized business aren't interested in nursing an engineer/developer/consultant for $16k/mo. They'll only be interested in maybe a half-day or day rate.
Even then the only value add you can bring to the table is to reduce costs for them. No one cares about how much effort or work you put in. You're not an employee to them. You are the consultant. They're purchasing an end product.
You either get real quick at being efficient or you're gonna wash out.
Large sized business would rather hire unless you possess some specialization they lack or is under market. So you have to punch above your weight class. Are your skills really worth $200/hr? If so, then you have the means to get those jobs by offering $100/hr. But, then again, if you were able to get that type of pay you would have just gotten a job.
To be independent, cashflow management is now the most important thing. Followed by your sales management. To then lastly your engineering skills.
All in all, it's likely your first 1 to 2 year you'll be making far under market until you've established a roster of clients.
The inevitability is that you'll have to turn to an agency model and hire others to scale. Which presents another series of problems to your plate. At that point you might as well just be another business manager hiring out technologists contractors who are trying to convince you that they're worth $100/hr that you then have to flip and sell for more than that.
Good luck.