1) Thanks for the thoughtful reply!

2)

Is the independently wealthy person likely to choose work over other uses of time, say, volunteering?

Probably not, it’s less likely. Outside income, regardless of the source, makes a person less likely to see going to work as a good use of time, and more likely to choose volunteering, hobbies, or television. People who receive outside income need additional incentive to work, compared to those who don’t. Imagine how much you would have to offer the wealthy person to get them to report to the office, instead of participating in satisfying volunteer activities.

whether or not we, as taxpayers, subsidize others via public health (etc) benefits, thereby allowing McD's to pay low wages, and also allowing those who use such benefits to accept jobs at McD's that would otherwise be untenable from a monetary perspective

I think the word “allow” is key here. People do not do something because it is merely possible, because they won’t starve by doing it; they choose the alternative that they judge will best satisfy their desires. If their desire for a warm bed is already met, it reduces their desire to perform work to get money to pay for a warm bed.

3)

The independently wealthy not only can afford to pass on a job offer

Exactly. Someone must accept a low salary in order for it to be a low-paying job. Outside benefits make a person more comfortable, and give them the luxury of being more selective in their employment. Almost everyone will work if the alternative is homelessness and hunger. If the alternative is unemployment with basic housing with basic food, some people will take that option (or at least quit their second job), and employers will have to make better offers to attract employees.