Customize BigCommerce checkout page for recreational fishing ecommerce business so that Shipping Method (Pickup or Shipping) is first question. If pickup is chosen use store address as shipping address so that sales tax can be calculated properly.

As an ecommerce business specializing in recreational fishing, I'm looking to customize the checkout page on my BigCommerce account. Currently, the layout is the default BigCommerce setup. I'd like to make changes to the layout so that the first question asked of the customer is the Shipping Method (Picking up from store or Shipping). If the customer chooses to pick up in store, I would like the store address to be automatically used as the shipping address so that sales tax is calculated properly.

I would like to keep the layout similar but make the said changes, and do not have any specific preferences for the new look. Although I would welcome guidance for the customization process, I'm not sure if I have any additional requirements or specifications.