The online documentation contains a lot of information about WebTest with numerous examples. The documentation of the steps is generated directly from the Java sources and therefore always up to date.
Additionally you can look at WebTest's Self Test Report to see how steps are used.Mailing list is the right place for all questions concerning WebTest. Most of the time you will get a very helpful answer within a short time.
Nearly every qualified Java developer with web knowledge should be able to understand how WebTest works within a short time and could be able to use and customize it as he/she needs.
Nevertheless the best commercial support for WebTest is surely the one provided by the people behind WebTest. With many years of experience in efficient web testing automation, they are the ideal source for the success of your WebTest projects.
Have a look at http://www.efficient-webtesting.com/ if you're looking for training, consulting or support with guaranteed response time.