I know of no way to do a bulk add, unfortunately. Perhaps there is through some sort of API or third-party utility, but not through any interface within Google Maps or Google Map Maker.
Google My Maps allows you to add custom points based on a KML file. My Maps creates a custom map that you can link to or embed in a website, but does not publish the features you add directly to the public Google Maps database - they are maintained only for your instance of the map.
There is no way to control which points show up at which zoom level in Map Maker or Maps. Only My Maps can do that.