Ecwid offers the performance and flexibility you need, with none of the hassles you don't.
RokEcwid component works as a bridge between Ecwid and Joomla!. In just few steps your store will be up and running.
If it's your first time with Ecwid, create a store is very easy. After you have created an account, use the Ecwid Control Panel to add your products and to manage the settings of your online store.
Once you are set with your store, copy the Store ID from the footer (bottom right) of the Ecwid Control Panel, like in the screenshot below. In this case it will be 1003.

After you have retrieved your Store ID, set it into the Store ID field on the right, in this page and save.

For more information you can check the Ecwid website, support and help pages.