wsad is kind of a special eclipse with lots of extra plug-ins especially for J2EE. WSAD has an integrated test environment. If you want to start with WAS from a developer-perspective the test environment is all that you need. You are going to need lots of RAM. It works with 512 MB but its much better with > 1GB.
There is a good book, which I find is well worth the euros/dollars/other currencies spent: amazon link