Have you looked into using FileMaker GO on the iPad so that it functions as a client of FM Server? That may avoid having to publish your system to the Web.
If you search the forum, you'll find that several people have been experimenting with an iPad or iPhone and a barcode scanner with FileMaker GO.
Thank you PhilModJunk for your suggestion, to answer your question why we intend to use the web interface: Isn't that the purpose of the FM-Server, so you don't need to buy any clients… a 100 clients (Filemaker GO) adding up to $3990…
Do you have any concerns about security with the Web feature in 'Filemaker Server Advanced'?