a) To get rid of the grey frame you need this:
background-color: transparent !important;
border: 0 none !important;
b) I would advise against inuttall's suggestion (as well as your request to make the images 100% of the content area). The images cannot be real larger versions, they'll only be blown-up versions of what the slideshow would normally display, so they lose quality.
A big part of the problem is that the WP slideshow is supposed to be 100% wide (including the grey frame), but 100% wide of the default content column only: it doesn't take into account the no-sidebar template (which is why your slideshow images were originally a lot narrower). If you aren't going to publish posts, i.e. if you aren't going to take advantage of the masonry layout of Visual, I suggest you switch to a theme that doesn't have a sidebar at all.
c) If you stick to Visual, or if you switch to any other responsive theme, you need to correct the widths you've set for the columns you have created. Responsive themes shrink to adapt to different screen resolutions and devices: drag the browser window to make it narrower and you'll see that the theme shrinks but your three columns don't. You need to set their widths as percentages instead of pixel values.