Show quantity selector
If you would like to show a quantity selector on the product page. There is always a quantity box in the cart.
Cart button location
You can have the cart button showing either above or below the product description.
If you are using the free Shopify app, Product Reviews, ticking 'Enable' here will show reviews below the product images.
You can enable related products, which will show other products from the same collection, and also enable 'Quick shop' which will enable visitors to browse details without leaving the page.