Customizing Twenty Fifteen theme

Hi We have chosen the Twenty Fifteen theme for our website, because it is the closest to how we want the site, however, when working with it, I have found that the Header image is in the wrong place (it’s the left sidebar) so putting an image there isn’t right for what we want. Also the backgrounds of the content areas we want a transparency on the colour there. I have included a link to a mock up, can this be accomplished using Twenty Fifteen as a base? Mock up: http://www.liff.org/liff/liffmockup.jpg Is there anyone here that is able to help me with this? Or is there a different theme that I can use to achieve what we want. Thanks