With the way it is now, you can only stock your shop from the myadopts page (I plan to add it to the shopCP at some point, but it is possible to make an alternate way in the meantime with the example code if you know how). The pastebin code gives an example of a section on a pet's manage page where you can add/remove them from your shop and for what price.
Item shops aren't available/made yet, so adopts is the only selectable option for now.
For the header image, can I see a screenshot? The image is appearing inside the url box?