Headers in Posts in Shop Isle Theme

I’m creating a Web site with the Shop Isle theme and I have two questions:

1) I don’t really need the e-commerce features of the theme. I just liked the aesthetics. So I turned most of that off. Will that cause me any problems with functionality?

2) I have a primary front page header that appears on almost every page throughout the site. However, when visitors click into post content, the header is gone and the post displays at the top of the screen and is cut off by the site title and banner.

I would like to either use the same header I have used throughout the site (chosen in Appearance), or prepare another custom header for the posts (articles) section of the site. But I can’t figure out how to add one. I installed the WP Display Header plug in, but when I choose to add the original header to the post page after installing it (option created by the plug in), the headers still don’t show up when I update the site.

Thanks.