Just to give one perspective:

Who actually writes the contracts, you or the buyer? What does a sample contract look like?

I joined a professional group that provides a variety of useful services, including starting points for common legal documents written by actual lawyers with actually informed notes about using them. So far I've not had a problem getting any clients to sign some usually simple variation of one of those documents. No-one has ever offered me a contract they'd written themselves; that sort of thing usually happens on larger scale projects than individual freelance/consultancy work.

Do you use a résumé or something more like a sell sheet when approaching buyers?

Ideally, neither. The best leads often come word-of-mouth via friends/colleagues in the early days, and then via referrals from former clients later as you build up a track record.

In what city are you working?

I'm based in Cambridge, UK. Some clients are too, others are further away, but all UK-based in my case.

Big biz vs. startups?

Ideally neither, if you're just starting out and going into freelancing alone.

Big biz is full of overheads and is notoriously bad at paying on time, and you won't be in a position to take advantage of the other side where big biz has big budgets available if you get to the right people and present what you offer in the right way. Your mileage may vary, but realistically it probably won't for quite a long time, unless you have some really compelling advantage that most people don't before you turn freelance.

Startups have the opposite problem. There is a much higher risk than average of working with people who lack professional experience and have wildly unrealistic expectations, who have relatively little budget to spend and therefore penny pinch at every opportunity, or who want you to put in the same kid of effort as they do when they own the business and you're just a freelancer who can be dumped in the time it takes to write a letter.

Obviously those are stereotypes, but if I were you, I would aim for the safer middle ground until you've learned how the game works. There are plenty of small/mid-size businesses who are established enough to have sensible money available but not big enough to have dedicated in-house people for everything. If you can get a few decent clients like that and do good work for them, you have a fair chance of repeat business and/or referrals that brings some financial security. If you keep your ear to the ground, you'll also start to figure out where you can really contribute something valuable, which in turn you'll be able to charge for at rates they consider fair even if they're way above what you thought you were "worth" because you took your old salary and multiplied it by 2.

What is your on-site vs. remote work ratio?

I work exclusively at my own facilities day to day, though I'm happy to make visit clients for meetings, presentations, on-site testing, or other useful activities that work better if everyone's in the same place.

This has a number of major advantages, including not getting dragged into areas outside my role or, heaven forbid, the politics in your client's organisation. Another big advantage is being able to take on multiple projects concurrently, which can be very useful if they are useful projects but no one project consistently provides the equivalent of full-time work. And of course, you get complete freedom in choosing how to set up your working environment, tools, usually working hours, and so on, which is a huge win for work/life balance and was my #1 reason for going freelance originally.