PremiumWP

Typically you find the best business style themes from commercial theme developers. Check here: http://wordpress.org/extend/themes/commercial/

you’ll find the widget codes in: wp-includes/default-widgets.php

be aware that if you make changes in those wp core files will be lost when you upgrade to a new version, so its not recommended.

additional widgets code will be found in the functions.php file of the theme.

Don’t know of any theme with a similar design, but it’s a fairly simple structure so it should be quite straight forward to create it. All the best.

Some similar would be:
Thesis
Catalyst Theme
Headway Theme

You will find a lot more choice of photography or photo blog themes if you look for premium / commercial themes. You could start here: http://wordpress.org/extend/themes/commercial/

Not exactly clear what your referring to there. Are you looking for the grey background image in your css as shown below?

#content (line 327)
{
background-color: transparent;
background-image: url("images/bg-content-top.png");
background-repeat: repeat-x;
background-attachment: scroll;
background-position: center top;
background-clip: border-box;
background-origin: padding-box;
background-size: auto auto;
min-height: 100px;
padding-top: 50px;
padding-right: 0pt;
padding-bottom: 30px;
padding-left: 0pt;
}

The instructions here about how to upload themes might help you http://codex.wordpress.org/Using_Themes