I would start paying attention to their "squatting behavior" around 18 weeks old. They will get more vocal and do a pretend egg song for a bit before beginning to lay. Then the combs will get redder and redder then they will begin to spend time in a nest and then they will lay.
I would say by averages you will see the BR's lay first, then BO's then EE's. But that is not an exact science for sure.
Yes. Sort of. You will need to encourage them if they are allowed to free range. If you have your nest boxes in or around your coop they will likely gravitate towards laying there. You can put golf balls or wooden balls that look like eggs in the nest around time of lay to help them figure it out as well. Most chickens will take to a nest box in the coop and they really like it concealed or private.
Free rangers will tend to find a secrete nesting spot so be on the look out if they are out most of the time. By and large they like to use your nest boxes you provide as long as their criteria is met. Hidden, private, darker, the smaller the better.
Yes indeed. They will lay in those for sure. That is a great set up. If you have any hens that try to lay elsewhere in the coop you can put a flap of cloth or something to that effect over the front of one of the nests to make it darker. You don't have to do this, just a fussy hen sometimes may test you.