1). You can try overriding the map's maxScale or minResolution property to allow you to zoom in beyond the canvas basemap's most detailed level. Note, when you do this, the tiles will be resampled when you zoom in beyond the last level and may appear pixelated, but it will allow you to zoom in enough to see the light poles layer.
2) You have a couple of options here. You can make a copy of the webmap in your Arcgis online account and change the symbology there. Then when you open your webmap copy, it'll have the updated symbology. Or you can continue using the existing web map but override the symbology in your app. To do this, find the AGSFeatureLayer representing the light poles layer in the AGSMapView, and override the renderer.