@Chris: To increase the site width to 1100px width, you can add the following css in “Appearance => Theme Options => Custom CSS” box.
@media screen and (min-width: 1025px) {
#page { width: 1100px; }
}
About the header image, I am not 100% sure if this will work on not. You can upload header image from “Appearance => Header” and then upload the image. Then you will see ‘Crop Header Image’ box. See this screenshot http://www.pinterest.com/pin/548594798331307420/ . Then you need to click on ‘Skip Cropping, Publish image as is’. This should load your original image you have uploaded.
To remove to gap, I need to check in your site URL. So, that I can check in and send you the custom css.
.
