So, for each product we create we need to either be able to choose which stores it appears in, rather than just a toggle to choose that it appears in stores, or in the stores we need options to choose which products appear or not on a store by store basis. As, at the moment it looks like you could make multiple sites with stores but they all would have the exact same products.

Next, we need each store to have categories and be able to choose which products appear in each category in each store.

Then we also need a way of choosing the order products get displayed by default (manually chosen order, by name A-Z or Z-A, by price, etc.), as well as offering the viewer options to change the sort order too.

Having something that can be added to the homepage of your site to show popular products. Perhaps with options to choose if it is based on views, sales. Maybe an option to display new products as a separate thing.

A product search function with a search page showing the correct products for that store, searching based on title, description and tags for each product, etc.

All product types should be able to be added to your store, even recurring products.

These are just basic e-commerce features. Anyone having different types of products and selling more than a handful would need these features so that the customer isn't overwhelmed with a huge list of dozens or hundreds of products they need to scroll through to find the one they want.