Sidekick: Set Up One-Page Checkout

Help me set up a one-page checkout for my Shopify store:

Store name: [YOUR STORE NAME]
Shopify plan: [BASIC / SHOPIFY / ADVANCED / PLUS]
Current checkout steps: [HOW MANY STEPS IN YOUR CURRENT CHECKOUT]
Average cart items: [TYPICAL NUMBER OF ITEMS PER ORDER]

I want to consolidate my checkout into a single page. Please help me:


  
    Layout structure - Design a one-page layout with all sections visible at once: customer information on the left, order summary on the right. Stack the information fields as Contact, Shipping Address, Shipping Method, and Payment in a single scrollable column.
  
  
    Enable one-page checkout - Walk me through the Shopify admin settings to enable the one-page checkout option. Explain any plan requirements or limitations.
  
  
    Smart field behavior - Set up autofill and auto-detect for address fields using browser autofill APIs. As the customer types their address, auto-select the appropriate shipping method and update the total in real time.
  
  
    Section collapsing - After a section is completed, visually collapse it to a summary line (for example, showing the confirmed email and address) so the page stays clean as the customer progresses.
  
  
    Express payment buttons - Place Shop Pay, Apple Pay, and Google Pay buttons prominently at the top of the page so returning customers can skip the entire form.
  
  
    Validation - Add inline field validation so errors appear immediately next to the relevant field rather than as a list at the top of the page after submission.
  
  
    Performance - Ensure the single page loads in under 2 seconds. Lazy-load non-critical elements and minimize JavaScript.
  


Provide step-by-step instructions for my Shopify plan level.