The HTML link is just an HTML link. The option in the configuration onle works with standard HikaShop "add to cart" buttons. So it's normal it redirects you to the checkout. If you want to stay on the same page, then you need to change your link.
That is your link currently:
http://paramipress.com/index.php?option=com_hikashop&ctrl=product&task=updatecart&quantity=1&checkout=1&product_id=1
That is want you should have to stay on the same page:
http://paramipress.com/index.php?option=com_hikashop&ctrl=product&task=updatecart&quantity=1&product_id=1&url=http%3a%2f%2fparamipress.com%2fbooks%2fmapping-the-dharma%2fmtd
As you can see, you need to remove the checkout parameter and add a url parameter where you need to specify the current page.
For the "next" button being at the bottom of the page, the problem comes from your template.
You have the CSS :
#main {
background: none repeat scroll 0 0 #FDFAF1;
margin: 0;
padding: 25px 20px 20px;
position: relative;
}
which you should replace by:
#main {
background: none repeat scroll 0 0 #FDFAF1;
float: left;
margin: 0;
padding: 25px 20px 20px;
position: relative;
width: 95%;
}
in the file
paramipress.com/templates/parami_template/css/position.css