Judie,
What format is your lat/long in? For ArcGIS Online, it needs to be in the WGS84 coordinate system. You may need to tweak it some for it to come in.
Unfortunately, AGOL does not behave as nicely as Google Earth does in terms of easily adding data to the map. But the difference is the power of GIS and what it can do and how it handles data.
The best situation for you, since it appears you will be continually updating this map, is to have a feature class (likely in the form of a Geodatbase like a File Geodatabase) in ArcGIS Desktop, and then continue to publish from ArcGIS Desktop in order to keep your AGOL map alive and up-to-date. This will give you the functionality that you need and provide the service that you need to provide.
I know you said you do not have this now, but that is really your best bet. I really don't know how trial licenses work when it comes to both desktop and online capabilities, but it may be worth looking into in order to get some data out there?
I am not sure if this is helpful or not but you may be stuck dealing with not being able to add audio to your popups for awhile, until you get more functionality, etc.