On embarkation on the Friends of St. Mary Belchamp Walter project it was suggested that the group need some form of on-line store.
In many respects the discussion on what "platform" we are proposing to use is a little premature as we don't have any products to sell or events to take bookings for.
On a first pass I don't see why we cannot have a "store" that is totally "home grown".
The key here is that you have Social Media presence in the first place! If you do then you can integrate UGC (User Generated Content) back into your website. I think that this is called "doing something cleaver on Social Media"
I am not sure how this works the other way around. For example, a Facebook button could take the visitor to your Facebook pages and then the visitor can comment there. On the other hand if an Internet users finds your Facebook page they may visit your website, but you need to get the visitor to comment somewhere (preferrably in a positive manner).
Like so many other area there are lots of enterprises that are happy to sell you a solution.