Dipesh

It is absolutely safe. Many of the websites use W3 Total Cache, it will help you speed up page loading and put less load on the web server.

In order to replicate the First page in the demo, you need to create a Home Page, select the Template for this page as Front Page Template.

The header placeholder is set to full-width with the recommended image width as 960px. Even though you have used an image 424 pixels wide, the rest of the space is occupied by the header placeholder.

The sidebar is part of the content area & thus shows up along with your posts and not header.