A very practical piece of advice! Thanks. This is roughly the picture I had in my mind about how to progress. My mother (who is a full-time consultant now) did this. She'd work at the government office during the first half of the day, then offer consultations during the rest of the day at a private establishment. She carried this on for several years and finally, when she retired from government service, she went into full-time practice and that seems to be working very well for her. The time-line of this is much longer than what you managed but I think her focus was never to quit government service asap.

Congratulations on where you are! I'd love for something like this in my career.