Pros and cons of (co-)authoring a reference book in early career?
I agree with the advice Peter Clark offers in the bit you've quoted. You're further along in your career than I am. (Defending in May). However, I've had many friends in your circumstances. Here are two things that I have gleaned from their experiences: 

(1) A mediocre book has little impact on the field, just like a mediocre journal article does, except that the book has such a higher opportunity cost.

(2) A bad book can actually be a kiss of death. People might laugh off a bad article, but if you put out a bad book, you might actually harm the good reputation you've built with your other publications. 

(3) To write a good book requires so much time, and such a high level of expertise, that it's usually not worth doing for a junior person. 

My sense is that these three sentences might not hold in all fields universally. Some fields are book fields where you are expected to publish the dissertation as a book. In those fields, I'd assume there's more reasonable expectations about book length publications. But in primarily journal based fields, I suspect (1)-(3) are true. 

Can you write the publisher and ask for a long extension so as to be able to keep a more reasonable research/writing schedule?