for the disclaimer, you would use the Server Validations porting CSS Form bulder to make the checkbox required.
for the comments, you will need to add a new comments column to the cart object, then in the add to cart button wizard, set the comments column to be updatabel from a text field, this will add the text box to the cart for the user to enter the comments.
When creating the cart display page, on the second step, you can select columns to add to the display, click the plus button and add the comments column. When you run the checkout wizard, the cart added to the confirm page and the emails will be based on the cart display page you create.