Do we start over again if we add Plus Web to our existing desktop software-only DBGalllery?

No! DBGallery's desktop software and it's Plus Web (a web-server plugin) all access the same database. The database provides the location of the image files so that doesn't change either. Many customers have used the desktop software for a while to get their image collection organized and ready, then add Plus Web to open selected areas of the collection to the web.