Yes you should be able to set the res lower, you will likely notice that text is not as sharp.
The computer will get warm during process intensive tasks such as gaming. You will likely notice that the fans are making more noise, they are running faster in order to dissipate the heat away from the cooling system. When you say top of the computer I think you mean the area near the hinge on the horizontal surface, not the top of the screen. I have never seen one get warm on the screen. I'm an IT professional that has purchased Lenovo exclusively for over 5 years, yet to see one hot on the top edge of the screen...