Size of product image and thumbnails on product page editable from admin panel. Specify any size you like, images don't have to be square - keep the aspect ratio.
It can also be a link to any page, e.g. link to a category with products from that brand, link to the search results or any CMS page (editable from admin panel).
There are sliders in Up-sell Products and Related Products blocks (visible if there are to many products). Now you can select as much related and up-sell products as you want,