I currently maintain a database driven catalog of about 1,000 digital & tangible products. I built the backend CMS and product database myself in Dreamweaver with Bootstrap, PHP & MySQL.
Customers are handed off to the 3rd party cart for payment processing. Upon completion, they're sent back to the main website to retrieve their downloads or confirm their tangible goods order.
I didn't build a customer log-in portal because quite frankly, we ddin't need one. But the backend CMS definitely has a secure log-in area for the CRUD pages -- Creating, Reading, Updating and Deleting records. As new products are added to the database, they're automatically reflected in the site's summary and detail pages.
Any shopping cart that gives you code for Add to Cart, View Cart and Checkout buttons will work under this model.