Deadlines add stress? Well, yes. After the first blush of enthusiasm wears off, the effort starts to look like work. -- and it is. You will likely need something to keep driving you steadily toward the end. Simple, but not unreasonable deadlines can help keep you moving on all the days you feel like sleeping in.

Set specific reasonable goals ion each deadline. Don't let yourself be diverted by every great but random thought that comes by, including any non-trivial editing. Jot down notes for later. Plan your work and work your plan. The deadlines will help keep you focused and on track. Otherwise you'll gradually find your book slipping further and more out of reach.