@benjo: It would have been easier if you had added your site URL. So, that I can check in and send your the css. For now, I just need to guess and send it to you.
1. If you just want slider and featured content in your homepage then you can add the following css in “Appearance => Theme Options => Custom CSS” box:
.home #content-sidebar-wrap { display: none; }
2. This is high level of customization and for this you need to build child theme. For child theme, check out http://catchthemes.com/blog/create-child-theme-wordpress/. Then after that you need to copy function catchkathmandu_homepage_featured_content()
to your child theme and change the position and all. For this, you might need to hire developer to work on it.
Note: Sorry for the late reply as we are still in state of emergency due to massive earthquake in Nepal. Internet, electricity, water and sanitation are huge problem here. We are also helping others in the community so we are slowing getting back online.