I use the same steps that Les outlined. All of the WA extension were designed to work together. Each one takes care of a specific task. The solutions were built with WA extensions, so there isn't a problem there either.
I put each solution pack in it's own directory.
In DW I create a separate site definition for the admin part. This makes it easy to work on one part at a time. You would use DataAssist to create the admin. I use the completed admin part to fill in the database so I have some data to use to test the public part.
You use Security Assist to protect the Admin pages.
eCart does the e-commerce part.
The link that Les provided has all of the specifics for each extension.
The guys at WA will walk you through anything you need help with.