Well, you can do the XML database and XQuery in a web-based application. But I don't think you would want to be opening applications like Finale from a web page. It might be better to use something like the Myriad Music Plug-in to display and play the MusicXML file in the web browser, and also offer the opportunity to download the MusicXML file to the user's machine. The Myriad Music Plug-in is available for free at:
I think that you would generally want a desktop application to be doing things like starting particular applications and reading in the MusicXML files. scripting all of that for different applications would get pretty complicated, though. You would probably need a macro program that records mouse clicks and other GUI actions across applications, and use that as a starting point. Good luck with the project!