I haven't created a feature layer from a CSV or XLS and attempted to edit it so I'm sorry but I can't help with that workflow. If you choose a different workflow you can create your feature layer via ArcCatalog then publish it to ArcGIS Online. Create the point with all the necessary fields, add it to ArcMap, sign in to ArcGIS Online (inside ArcMap - File - Sign In). Then publish the point feature class to ArcGIS Online through File - Share As - Service. Follow the wizard steps (see Help if you need guidance on these steps). When complete the point is available on ArcGIS Online as a feature layer, you can add it to your map, edit it, etc.