01. Try using the Theme’s Layout Builder you can create Custom Layouts for WooCommerce pages like Checkouts. So, you can use that to create your own custom layouts for the checkout page.
02. You need to find a third party plugin to achieve more functionality that best suits you. We have not tested such kinds of plugins, so we don’t have any detailed suggestions https://woo.com/document/whatsapp-chat-for-woocommerce/