You can use all function groups, remote functions, BAPI and XML messages about 10,000 to 20,000 as Web Services providers. There are wizards, which create Web Services in very short time.
NW WSA has about 300-500 WS in MySAP and R/3. All documentation is at help.sap.com websites.
You can prepare and structure your company for ESA pilot project and later to deploy ESA to all your company business areas and business processes by using SAP Solution Composer.
In this way you can significantly improve your company result - may be 30% ?