Hello,
Here below some answers for your question:
1- SharePoint Foundation can run a webfacing site.
2- You can configure Foundation with FBA.
3- You will need to purchase a license called External Connector for Windows Server in order to run the SP Foundation as a web site, for more information check out this:
http://www.microsoft.com/windowsserver2008/en/us/external-connectors.aspx and it's not that expensive in comparison with SP Server Internet License.
4- you can configure the anonymous accessed pages mixed with non-anonymous pages.
5- You will loose all the publishing features in case you need it, the WCM features only exist on the SP Server with Internet License.
6- You will loose all the server features such as InfoPath Form services, excel services, etc...
Mohamed Saleh [SharePoint Server MVP]