I don't know if these forums have a limit on the file size that can be uploaded. Perhaps you can upload one of your smaller shapefiles.
As far as the size of shapefiles that can be supported in a web map, it's roughly 1000 features *total*, across all shapefiles being loaded into the map (not 1000 features per shapefile). It can be less features if, for example, uploading polygon data with a lot of vertices.
Mike