Hey there,
I would advise you to have a look at our demo site and on the left you have an option to launch a live demo instance. It will give you access to the backend of the component.
You are able to submit locations from the frontend as seen here:
demo.compojoom.com/hotspots/submit-a-location
You can notify administrators per email about new hotspots, but you cannot have like a member moderation. This needs to be custom build. If you need this you can request a quote here:
compojoom.com/services/joomla-development
If you look on our demo page you'll see that in the menu we load 20 hotspots (you can set it to 100). Other hotspots are loaded as tiles (the small markers). The information about those is cached in images, in order to speed the map. Then when you hover your mouse over an area in the background we load the information about the locations currently on that tile. You can read about all this in our docs (scalling for large databases)
It is the first time that I hear about iJoomer, but version 4.1 will work just fine on a mobile phone, so there won't be a need for an app. (it already works fine on ipad)
Regards,
Daniel