Should I install Windows 10 first and then do a BIOS update or should I update the BIOS first? In your case it doesnt matter. Some instances an update is needed for stability of installation.

Do I need to update my BIOS before installing Windows 10?

Unless its a new model you may not need to upgrade the bios before installing win 10.

Do you need to update BIOS for new PC?

In general, you shouldn’t need to update your BIOS that often. Installing (or “flashing”) a new BIOS is more dangerous than updating a simple Windows program, and if something goes wrong during the process, you could end up bricking your computer.