Hello.
1. To display products by default in list view, just edit your menu item and in the Page Display tab in the Page Class field add the class product-list-layout
2. Currently the reviews are in a tab because the content is long due to the form and if the product has reviews it will be longer so as not to be able to be in the Add To Cart section. Or do you want a button that when you click on it it will automatically take you to the tab? If so, you need to edit a file to know which one you need to know the exact place where you want to display the button. You also need to know Javascript to make that button open the review tab.
3. From what I understand, you want the product image to be displayed in grayscale mode when the product is out of stock. To give you an adequate answer we would need to see a product that is out of stock, because if it has a class that indicates that it is out of stock, you could simply add disabled using javascript, so that it is not navigable or with CSS make the image gray. Now if you don't have a class you can also do it using javascript, or if you prefer directly you would have to modify files.
Regards
