You can have all your symbols on a single symbol layer, or you can separate them out by type (for example, you could have your train station icons on one layer and your restaurant icons on a different layer). How you organize your symbols is up to you and is dependent on how you want to style your icons or text labels. Icons or text that are styled the same way can typically share a symbol layer.
- Mapbox Style Specification symbol layer documentation
- Mapbox Maps SDK for iOS symbol layer documentation
- Mapbox Maps SDK for Android symbol layer documentation
Examples of how to style symbol layers: