WID/WPS is actually pretty simple. The original intention was for analysts and business people to "compose" services (DO NOT LET THEM DO THIS!) so the UI is simple and easy.
Most of the work will be in defineing and implementing the back end services which depending on the platform will mostly involve wrapping existing code in SOA service.
The most important thing to bear in mind is that SOAP is technoligy and SOA is an architecture and a state of mind.
There is a zen to a succesful SOA implementation. Its all about "business services", if you have a service that you cannot describe to a business user in less than six words you have done it wrong! Ideally the service name alone should be enough to describe the functionality of the service.
If you end up with a service called "MyApp.GetContactData" described as "get name, addresses tel fax etc." then you are there. If You have a service called MyAppGetFaxNoFromOldSys" described as "Retrieve current-fax-nmbr from telephony table in legacy system" you are doomed!
Incidently most of the Websphere tooling for WS* is pretty nice. But I would recommend the very wonderful SAOPUI tool from http://www.eviware.com which is very good for compsing/reading WSDL based messages and also function as a useful test client or server.