Website Advice - Complements App

Hi All
My app is 90% done and am beginning to think about a website.
The site will be quite small with several information pages and a blog…mostly information around using the app.
It will also be integrated with Backendless so app users can log in to their account and view certain information stored with Backendless.
The app would be distributed in the AppStore and Play
So I think building the webite with AppGyver would be fine, except for one thing. I would also like a page where I sell a very limited number of accessories (5 or 6) so the site will need ecommerice functionality…card payments and similar. And I dont see how I could do that using Composer Pro…
Any advice, tips, or suggesstions would be greatly appreaciated! I have looked at Shopify for instance and a site there would require visitors to log into their account on the Shopify store, which would mean I would have to add a flow to create both an app user AND a Shopify user when someone registers with the app…sounds cumbersome.
Thanks
Paul