1) You would need to use data assist to create the Products insert page where you can assign the product to the category.
Run the data assist wizard, and select the products table. Set category column to be a menu, click the lightning bolt next to the menu and select the categories table. Set the category ID to be used as the value, and the Category name to be used as the label.
2) Site Import is not able to download the source code of site files, it will only download the browser content, the HTML that is generated by the PHP processor and sent to the client browser. If you want to study the PHP code of the power store pages, you will need to buy power store