As AL said poodle is very helpful in Moodle for creating and posting and using files. It is very nice to have things put into the activities in Moodle so you are not juggling several different programs outside Moodle.
I would put as many of the audio files in Moodle as I could if you are wanting to share. I don't have problems with my iPhone or my iPad with audio files (MP4) when they are in a Moodle activity. I would mostly have them in activities. Activities are not difficult to share. If you wanted to share them with teachers who would be using the same ones for multiple Teachers In multiple activities you might have a resource course for teachers with a database activity where they are uploaded and can be searched and downloaded.
As for having multiple courses with older elementary students I would probably have a main course with different topic areas for the areas we are using Moodle for and listing homework etc. Then put a link out to another course you want them using. I would probably only do this for the subject areas or a special unit that I was going to use quite a bit or that I really need students to go back and look at previous work or resources for reference. It will take some training to get them used to where you want them to be if you do this.
I hope that helps some