Hi,
For the background, you can use this property:
#hikashop_category_information_module_129 div.hikashop_subcontainer{background: none !important;}
To put the picture in the center, the problem come from your template and the properties: ".div.dewinkel-block img", "div.dewinkel-block img" which have margin.
How do you configure your breadcrumbs module ? I suggest you to display it on all pages except some pages, by this way it should be displayed everytime.
For the newly added products, HikaShop select the products the most recently added. You can't set the period, you can just restrict the number of products displayed.
You could maybe edit the request which is selecting the products by adding a new where condition, for example where "product_created < $oneWeek". And $oneWeek = time() - (7 * 24 * 60 * 60);