All those options create a fair degree of complexity so let us help: We'd be glad to help ascertain what you need and advise on the best license for you.
While you're here, let's cover a few of the basics for reference:
FileMaker Go for the iPad and iPhone is free. However if you connect to a Server with FileMaker Go you’ll need to buy enough “Concurrent Connections” to cover the number of people that will be connecting at any time.
WebDirect is the same: you need to allow for the number of people that will be connecting to the server at any one time. (This reflects the purpose of WebDirect as a means for defined workgroups to access the database rather than high traffic or public websites.)
FileMaker Pro can be purchased outright which is an option if you have just 1 - 3 users. Beyond that we recommend the Annual Volume License Agreement (AVLA) which kicks in for 5 licenses. This is essentially a rental and must be paid annually to keep using the software, which is in the long run the most economic option.
If you’re hosting FileMaker yourself you’ll also need a license for FileMaker Server, which can also form part of your AVLA.
There are other options — including site licenses, outright purchase, and Education/Non-profit discounts. We’re more than happy to advise and now offer a procurement service to manage your licensing.