Three pages that should be enabled for the Guest user profile for a storefront to have anonymous checkout are:
* CCPaymentInfo: This page allows the guest user to enter their payment information, such as credit card number, expiration date, and security code. The page also displays the order summary and total amount.
* CheckoutNew: This page allows the guest user to enter their shipping and billing information, such as name, address, phone number, and email. The page also displays the cart items and shipping options.
* OrderConfirmation: This page displays the confirmation message and order number after the guest user places their order. The page also provides a link to view the order details or print the invoice. Salesforce References: B2B Commerce and D2C Commerce Developer Guide, Anonymous Checkout

Explanation
Version related upgrades are passed on to subscriber API extensions/overrides by using the "delegate" keyword, which allows inherited method calls access to the most recently specified service version. For example, delegate.getCart() will invoke the getCart() method of the latest service version that is available for the current storefront. This way, extensions and overrides can leverage the new features and enhancements of the upgraded service versions without modifying their code.

Two things that happen with the cart during tax implementation are that new entries are written to the cart and previous entries are deleted from the cart. A tax implementation is an integration that calculates and applies tax rates and amounts to a cart or an order based on various factors, such as product type, price, quantity, location, and tax rules. A tax implementation can use either an external tax service provider or custom Apex code to perform the tax calculation. When a tax implementation is invoked for a cart, it writes new entries to the cart with a type of Charge and a charge type of Tax. These entries represent the tax amounts and adjustments that are applied to the cart. Before writing new entries to the cart, the tax implementation deletes any existing entries with a type of Charge and a charge type of Tax from the cart. This ensures that the tax calculation is accurate and up-to-date based on the current state of the cart and avoids any conflicts or inconsistencies with previous tax entries. Previous entries are not copied to another object or modified with the new tax calculation, as these are not valid actions for handling existing tax entries. Salesforce References: B2B Commerce Developer Guide: Tax Integration, B2B Commerce Developer Guide: Tax Calculation Flow

A theme can be enabled in Salesforce B2B Commerce in three different ways:
A Storefront setting: The theme can be specified in the Storefront Configuration settings in CCAdmin. This will apply the theme to all users who access the storefront.
An Account Group field value: The theme can be specified in the Theme field of an Account Group record in Salesforce. This will apply the theme to all users who belong to that account group.
Dynamically through a hook: The theme can be specified dynamically by extending the cc_hk_theme hook. This hook allows changing the theme based on various factors, such as the user, cart, product, or storefront. For example, the hook can apply a different theme for a specific product category or for a specific user segment.