Hi,
Hope you are doing fine..
The first thing I'd like to say is if you are looking to build an eCommerce site with similar UX and UI of eBay you should go for custom PHP with CI MVC instead of using any CMS. However, we are open with any updated CMS like Magento, Shopify, WordPress with WooCommerce plugin, etc. But to be very honest with you, I'd like to propose you to build it from scratch using PHP with CI MVC framework to make your site utmost secure, stable and user friendly.
The site will be Responsive at every pixel and properly optimized for SEO. The GUI will be user friendly, eye-catching yet sleek and professional with fluid navigation.
We'd build a user friendly ADMIN PANEL so that you could easily manage/update the user accounts, reports, payments, images/banners, sales, etc.
Finally, after the development, we'd assist you to host the site on your server and provide you 3 months of Free Support after the site goes live.
So please revert back to us with your valuable comments & thoughts. We're really keen to work with you.
Thank you
Robert Parker