Depends on what what you requirements are. OpenAM feldlet or Shibboleth i probably the best approach since you don't have to do so much coding on your own.
OpenSAML is a very low level toolkit for handling SAML messages. I would not recommend it if, not really needed.
As for the things they are asking for, the AssertionConsumerServiceURL is the service endpoint where you recieve your SSO SAML messages.
Defenition of AudienceURI is quite gray. Basically you send them an identifier, they include this in their messages and you validate that identifier is the same you gave them. I my self do not understand the difference between this and Destination...
I'm a bit surprised that they ask you for this. The standard way to do this first exchange of information is by SAML metadata documents.