2. You use the BIOS (or the BIOS patcher) if you are flashing your Xbox and want it to permanently connect via VGA. The dual boot softmod is fine. The boot disc allows you to switch between VGA and other video connections really easily.
3. You'll still also need a component cable for the Xbox, and three female-female barrel connectors. And I'm not entirely certain that the component cable will put the video chip in the right mode for VGA (HDTV is mode 2+3, VGA is mode 1+3 - have a look here
). You're better off with a Frozen cable, because that definitely puts the video chip in the right mode.
4. No. The boot disc makes the output RGB. (FYI, it's entirely unrelated to the sync mod).