With single purchase of any product, you are licensed to use the product on one store only. If they are running several stores on a single PrestaShop installation with prestashop’s multi-store feature, you need to purchase a separate license for each store.

You can set up your site locally or on a temporary domain, and then move the entire site over to a live domain. How to move? Tutorial for presatshop 1.6 and presatshop 1.7.