Hello!
My client has a website on Showit and we would like to add a shop. Can anyone tell me if Shopify ‘Starter’ is suitable? My plan is to add the pages on Showit and then embed a buy button and checkout. Can this work when products are customisable (IE. Different sizes?). Is it possible to embed an entire product listing (name / image / description) instead of a buy button?
Thanks 
Shopify only offer to embed the Product Cards to the third part CMS with the help of Buy Button.
But if you want a way where you can embed the whole product from Shopify to Showit then Shopify official doesn’t provide this option.
You may take a look to the third party Plugins. But my advice is to sell only on Shopify instead of Embedding it on the other CMS.
Please let me know if you willing to use the Shopify or Showit with the whole product embed?
If you could answer me then I can move further with providing the Plugins that may help with whole product embed.
Waiting to hear back from you.
Thanks
Shopify offers a Buy button that allows you to embed it on a Shopify website. You can check this article to learn more
https://help.shopify.com/en/manual/online-sales-channels/buy-button?utm_source=chatgpt.com