The maximum grade is simply the 'out of' grade you would get on a test back when you were in school. When making a quiz, your quiz questions can be individually assigned a value, but the sum of the questions will proportionally adjust to what ever value you have as the quiz's maximum grade. This is the same for assignments -- if you use a rubric or grading scale, the sum of the criteria values will proportionally adjust to the value you set as the assignment's maximum grade. I would imagine that would effect the weighting, but I don't use weightings so I'm not sure.
One reason there is a maximum grade (for assignments) is because you can change your settings to allow more points than the maximum, thus awarding extra credit if a student scores more than the maximum grade (a 105 out of 100).
"I don't know if I should be setting the max grade of these quizzes to 100, or if I should be setting it as the number of available points (127, 112, etc) in the quiz. "
I would think this would be completely up to you/your school. How are your courses designed? Our Quarters are each worth 500 points.
One reason there is a maximum grade (for quizzes) is to help keep sanity with your gradebook. We update our quizzes a lot, so having the quiz max grade equal to the number of points all the questions are worth is not a practical method for us since we are frequently adding or removing questions. There are times the sum of our quiz questions exceed what we would actually want to have as a maximum grade--ie. our Driver's Ed class is required to have a 100 question final exam (1 point per question), but we only assign a maximum grade of 50 points for the quiz. We like to keep our quizzes totals simple (10, 15, 20, 25 points) so it's easy for us to make the quarter total 500 points, even if we add questions to our quizzes.