The images will adjust themselves to any block so there is no need for a specific size of the images. However, too big images may cause your page to slow down, so please upload images whose width are no more than: For desktop: 1920px For tablet: ...
Currently there is no direct way to import your existing Shopify pages into Tapita. They would have to be rebuilt using Tapita page builder. However you can contact us to get your pages built for free by our support team.
You can follow the steps in this tutorial to do so: https://tagembed.com/support/embed-rss-feeds-on-html-website/ In Step 3, use Tapita's Custom HTML element.