Where can I set the width of the actual content of the window (Theme Parador)?
You mean the width of the main content? There is no option for it. Do you want to make it larger or smaller?
Where to set the width and height of the photos for the slider?
The images in the slider are always as big as the images are, means if you upload images with a size of 1500 x 700 pixel, the images are 1500 x 700 pixel in the slider.