Create a multi-step drupal 8 webform including a stripe payment

The project consists in creating a multi-step ajax form on a drupal 8 website.

Step 1 is a multi-choice (with 3 options)
Step 2 calculates a price according to what is selected on a radio button field
Step 3 is a two field form (telephone and mail)
Step 4 collects and charge a credit card to Stripe

A mockup is provided (use for description and design).
Our website is hosted on Pantheon.io ; having your own access to this platform is a plus.