We are in the process of making some important technology decisions for a social networking application. We're planning to have Cassandra(a NoSQL database to support efficient data storage). We would be using Hector(a Java client) to interact with Cassandra.

1.) Would Java EE be a good choice over PHP for a social networking application in terms of performance, scalabilty & complexities?

2.) Another possible implementation strategy, Is it suitable to have backend alone in Java and rest in PHP?

3.) What differences(as compared to PHP) it makes in terms of costs at various stages of application development, deployment and maintenance ?

4.) What are the things to keep in mind as we move along with Java development& deployment(as we are relatively new to the Java background) ?

5.) If you could list some major production deployments of similar type(social network) applications in Java.

Thank you!