Eclipse

The one the eclipse run in is the default java installed in the system (unless set specifically in the eclipse.ini file, use the -vm option). You can of course add more Java runtimes and use them for your projects

The string you've written is the right one, but it is specific to your environment. If you want to know the exact update then run the following code:

public class JavaVersion {
  public static void main(String[] args) {
    System.out.println(System.getProperty("java.runtime.version"));
  }
}

What I would like to do is use Eclipse for (...)

The Eclipse IDE for Java EE Developers allows to do what you're asking for out of the box.

Should I download a totally new version from Eclipse site or can I just ADD necessary features/plugins to my current Eclipse setup.

Both would work, although it would be simpler to just get directly the Eclipse IDE for Java EE Developers (especially if you don't know exactly what plugin(s) you're looking for). Personally, I don't use the version you can get from the repository but download Eclipse from the official website and install it in user mode.