Also Base 8 dimensions are also more efficient and render a tiny bit faster. I'd say 2048, user could downsize it for less "Hi Rez" use.
Just my opinion but I'd say max file size of around 1 to 2MB.
You mean as in DPI? Then I'd guess 72 dpi - I don't think Bryce uses any more then that or converts the size back to 72.