– resize the page layout so that the entire bootstrap slides are visible without scrolling down?
The slider image width is set to 100% ( which is the layout width ) and slider height is set to auto.
All you need is to upload an image that’s height does not overflow.
Resize your image before upload.
– set a background color on L/R side of the main content section?
It only possible to set the background color of the entire site.
I can see that you have already set a background color for your website.
Cannot divide website background color into sections.
– remove the space between the logo header and the menu bar?
Try Theme Options -> Header -> Header Padding Top and Header Padding Bottom
– remove the grey line from the middle of each page?
Which line are you referring to? There is no line in the middle of this page.
Please provide screenshot with annotation.