Map-based website

I want to create a new map-based website that allows registered users to drop pins (with a description and photo), which would be grouped into layers. This could look a bit like a Google 'MyMaps', but I would need unlimited layers (and don't want users to be able to export the data). Also some sort/search functionality on the layers. We would need to assess the best underlying map to use to maximise potential views while minimising licensing costs. Please let me know what experience you have with such maps.