I was writing an e-commerce platform about 4-5 years ago for my ex company and it was in pure PHP + PostgreSQL + jQuery and JavaScript. This was only the store part, as back-end was administered through desktop app(don't ask my way). Today I will probably go with PHP Symfony framework pure as an API and some JS framework(Aurelia is my favorite so far), or maybe full in Node.js.
For the database part I will stick to standard RDBMS systems that are web hosting out-of-the-box available like PostgreSQL or MySQL(using things like DoctrineORM for PHP you don't have to worry about either of those on development level), and I should avoid NoSQL stuff like MongoDB, because e-commerce sites tend to grow with data-products far more quick than other stuff like blogs, and for that I would use something more robust, stable and mature than NoSQL database. Maybe I am wrong considering my experience with NoSQL. But I don't have anything against MongoDB, learning it now and I am very into it. :)
For the e-commerce platform from ground, you should consider already existing projects for guidance (coming primarily from PHP background I don't know if there are any open source projects in ROR), but you can look into things like Sylius or Elcodi/Bamboo . If you need some guidance about database organization and patterns, you can contact me if you like and I will be happy to write you a little helper on that. :)