hi,
1) not as i know of by CSS, but you can achieve this by editing the attitude-pro/library/structure/header-extension.php file.
Around line 266, find this one :
<img src="<?php echo esc_url( $header_image ); ?>" class="header-image" width="<?php echo get_custom_header()->width; ?>" height="<?php echo get_custom_header()->height; ?>" alt="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>">
Add your link to this line, example:
<a href="http://www.archcityhomes.com/"><img src="<?php echo esc_url( $header_image ); ?>" class="header-image" width="<?php echo get_custom_header()->width; ?>" height="<?php echo get_custom_header()->height; ?>" alt="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>"></a>
This should work
2)i don’t know
3) not by custom css for sure, but by editing the structural files of the theme, it is possible, but i don’t know how, sorry