You should be able to see the attachments in the Universal Email server behavior in the attachments tab. In here do you see all the files listed? It might be best to test with two and make sure you get that working before trying with more.
When you are adding in the other attachments you will need to ensure that you have the full server path to the file as well as the file name. Have you been able to confirm that the files were uploaded prior to sending them in the email? Please post back with the code you have in the server behavior for the attachments.