Reply To: Related produts in single product page

Hello,

Related products are displayed as per tags not categories. You need to create a tag for each category and link the products.

You will find the options to set the number of products in the row in the Theme settings > Product page > Hide/show elements https://gyazo.com/068102f1db10e7bf894a992b6c1e0035

Here is the instructions on how to edit product tabs: https://docs.woocommerce.com/document/editing-product-data-tabs/

Best Regards