Ask HN: Responding to a “blank canvas” job offer?

I'm a freelance developer, reasonably successful on the business side (6-figure annual net revenue, varied and interesting projects).

An enterprise client of mine that I really enjoy working with (on a contract basis) has tried to hire me as a full-time employee on more than one occasion, and I've gently, gratefully said no, as I value my independence, and generally want to continue in the entrepreneurial vein (for example, growing my consulting business by hiring employees).

They've asked me again, and basically asked me to set my own terms, including:

- scheduling flexibility (work for them only part of the week/month/year)

- contractual freedom to continue running my business when not working for them

- salary & benefits

Given that I'm already doing lots of contract work for them, I'm considering the options here while obviously trying to balance them against opportunity costs.

Salary aside, what would you ask for in this situation?