It sounds like you are making a projector that will play fullscreen, not in a browser?
If so, then you can make the project the same size as the resolution of the display, or a percentage thereof. 1680x1050 is a different aspect ratio from 800x600. You could make the project 1/2 the monitor size (840x525) if you want it to be smaller. That would be a good size if the project will also be viewed online.
Yes, my project will only be displayed on the monitor.
Thank you very much for your help.