How do you make the best use of a prospectus colloquium or other landmarks along the way? How do you work with advisors to get the best help from them?
Choose the advisor who will be toughest on you, within your tolerance range. (Don't choose the junior person just because you think that person will be more lenient or less intimidating.) Look for someone whose style of time management fits with yours or at least will have clear expectations about deadlines and turn-around times for reading chapters. It doesn't much matter whether the person has a turn-around time of 3 weeks or 8, if there is some consistency. The best guide is how fast that professor turned back papers in seminars. You should plan to turn in things regularly and get them back regularly. That is the key to a good working relationship.
For other readers of a dissertation, you should look for alternative perspectives, but ones that are complementary and don't pull you too much in other directions.
The exam or meeting at which you discuss your proposal with your committee is a time to listen to what the committee is saying about the viability of your project. It's a very useful "landmark" and will also tell you how helpful your committee is going to be. I have no specific advice except to listen very closely to the questions behind the questions. Ask for clarification later. "When you asked me this, were you implying that I should be looking more at this kind of issue."