This may not be the "right" way of going about editing your theme, but it worked really well for me and was pretty simple.
I copied the existing twenty eleven style.css sheet and pasted it into my child theme, then I went through using Firebug to find all the colors etc. I need to change. This is really easy if you open your style sheet in DW code view, because Firebug will give you the style sheet line (for example line 527).
I'm not sure what you mean by "logo" but if you mean where it says Dev at the top of the page I don't know how to cut down white space without removing the top header section completely. When you go into your header file (copy and paste it into your child theme just to be safe) remove the following code:
<h1 id="site-title"><span><a href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></span></h1>
<h2 id="site-description"><?php bloginfo( 'description' ); ?></h2>
This will remove the whole section above the header image. Then remove the second appearance (there are 2 total, leave the first) of:
<?php get_search_form(); ?>
I hope that helps!!