I believe that the first testlet is of moderate difficulty.  The difficulty of the second testlet is based on your performance on the first testlet.  The difficulty of the third testlet is then determined from your performance on the second testlet.  If you perform well on the first testlet, for example, your second testlet will consist of more relatively difficult questions.

A correctly answered difficult question contributes more to your overall score than a correctly answered easy question.

On the sections with simulations, the MC are worth 70 points with the simulations making up the rest.  I think the written communication is worth 10 of the remaining points.