Makiing CS4/AS3 Site, need some advice please

I’m making a site in AS3 for a client, and have some general questions before I begin.

Im using SWFfit ( to resize the flash site properly for any screen size and was wondering what I should set the default width*height at for the original flash site. Also please take into account that it is being dropped down 80 pixels for a HTML header bar with logo and contact info (so that it loads instantly, and will appear even if flash not installed or on mobile site).

Any suggestions? Thanks