1. the ‘borders’ are partly generated by the background image for #page:
http://ourconstitutionalrights.com/wordpress/wp-content/themes/default/images/kubrickbg-ltr.jpg
btw: any border style of #page in style.css will be overwritten by the embedded style with ‘border:none;’ generated in header.php.
2. for images in the sidebar, most use the textwidget, and insert the image code there. image paths need to be absolute to work.
there is no problem to have html images above background images.
3. yes
4. don’t know about the ‘best’ - this is the main article:
http://codex.wordpress.org/Template_Hierarchy
and you may find some info in here:
http://codex.wordpress.org/Theme_Development
and follow the links within these articles
alchymyth on “Problem: border-right on #page. Question: image in sidebar”