When the time comes, your employer might prefer you going part-time rather than quitting altogether. This goes without saying, but you should definitely ask. I hope you're pleasantly surprised.
MMM and Mrs. MMM basically did the part-time two-income thing, where he would do various construction work, and she would do real estate. From your numbers, it looks like you won't need to work at all in maybe two or three years, so you might could just quit and take whatever opportunities come along without worrying much at all about income.
My plan is to ask to go part time, and at the same time, my wife will try to break into the adjunct teaching gig. Speech pathology seems like it could scale well, simply by limiting the number of clients. It's hard to suggest part-time gigs for you without knowing your skill set. Could you tutor or give lessons in something? Do a web search for part time work and share with us a few items that pop out at you, and we can give our opinions. Would you want to do a limited number of hours per week, or would you want to work a few weeks and then take a few weeks off?