Ask HN: How would you negotiate a part-time software engineering offer?

I'd be interested to hear from both employees and employers on this:

I'm a full-time software engineer looking to transition into a role where I can work a little bit less per week (24-32 hours) so I can dedicate more time to passion projects.

Regarding salary and benefits, what is reasonable to expect if you're transitioning into a new role as a part-timer? What is reasonable to ask for once an offer is extended?

For those of you with experience working part time or hiring part time employees: Was the compensation full-time salaried or hourly contractors? What was the income delta? Was health insurance part of the compensation package? How about PTO?

Thanks!