Hi, If you send us a message to support@contentful.com we'll be happy to help you with determining which API to use etc.
You can read how Nasty Gal brought together content and commerce with Contentful here: https://www.contentful.com/blog/2014/09/12/Marrying-Content-and-Commerce-How-Nasty-Gal-uses-Contentful/ (They used our Ruby Gem: https://github.com/contentful/contentful.rb )
Cheers,
Christian