Bingo! I've done it twice to my former employer in the past two years --full-time to half-time and now no-time-- and both times it felt incredible knowing that I'm FI.I’ll tell you though there is tremendous freedom in knowing you can walk from a job anytime you want.
Awesome that you're interested in coaching and volunteering. I often volunteer with road bike, mountain bike, and trail running races in our area. Sweep and SAG can be fun, but we tend to prefer aid stations. With practice, it takes no time to set up an aid station, so it's easy enough to get a workout in before racers arrive. Then you get to spend a few hours in the shade (often with great views), handing out food, drinks or otherwise helping folks along with their day. Such a great way to spend the day.
Best of luck to you!