I would make a copy of your entire site in DW, and develop the dynamic site separately. That way if you hit a snag, you can upload the old static site in a pinch. Takes the stress factor down a notch.
Install a local testing environment:
Get the eCommerce database here:
Use DataAssist to build the backend.
Enter your current data into your new database so you will have something to test with.
Use eCart to build your search and results pages using the tutorials.
Update your links to use the new pages.