You need something like Multi-account Containers in Firefox to fully isolate Facebook from anything else. Basically if you are signed into Facebook in the browser, they can track you across any sites that use their Like buttons, comments or just tracking pixels. Some of it is blocked by Privacy Badger, FF built-in tracking protection and the like, but not all. By using a container to isolate Facebook's session from other tabs, you can prevent that.

You have little control over businesses transmitting purchase data to Facebook or other data aggregators.

Best you can do is withhold information at time of purchase. Use cash, don't give your email, phone number, etc.

Some businesses are clever and dangle a carrot with the request for PII such as emailing you the receipt or texting you status updates. You will have to learn to be "that guy" and politely refuse, or give bogus information.

None of them. You sign up to a website, they'll get your name, username, email and turn it over to FB.

I made the mistake of using the same "throwaway" email address for Facebook as all my online orders. Of course many of the stores uploaded their data on me to Facebook...

The bitchy thing is, even an Android app like MX Player or Maps.ME was sending events to Facebook, but FB's JSON just said "custom event"...