1. This doesn't matter too much since SiteAssist Professional is reenterable. After running through SiteAssist the first time, you'll need to replace the Dreamweaver template used by your PowerStore files with the .dwt SiteAssist created. Then when you update your site, your PowerStore files should take on the same look and feel of your SiteAssit site.
Please note that because SiteAssist Professional has so many different styles, some might work better than others. You may need to customize the SiteAssist template in Dreamweaver if additional editable regions are needed.
2. Yes, the lock icon appears because the files are "read only" by default. Locate the files on your computer, right-click on the root folder and choose Properties. Then, uncheck Read Only, and click OK. There is no need for any of these files to be read only once you start making modifications.
3. The Streamline design is an additional design provided with your purchase of PowerStore. Go to your Download Center, expand the Graphic Files option and download the Streamline Web Site Design files. You may find applying and customizing this design more straightforward than using SiteAssist Professional, but i suggest you use trial and error to achieve the desired result.