There are many good sites - in fact you are on one. 
Air exchange - It depends. I view my eggs Wed and Sat which are the days I exchange the air. Now, my incubator has air exchange capability, but it tends to dry he eggs out a little. So I have disengaged this feature. I wipe the windows during this time so I can see how quickly they "sweat" again. This gives me a good idea of the relative humidity.
On or around two weeks before they are due to hatch, they will collapse. Also, keep in mind that as the incubation advances the eggs may heat up enough that you have to lower the temp of your incubator - if fixed.
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Jay A. Martin