They are totally seperate so it really makes no difference what you do first.
Unless theres a particular reason to flash the BIOS I wouldn't do that though. The usual reason to update the BIOS is to support newer CPUs that weren't available when the motherboard was created. Unless this is the case or there is another problem which a BIOS update will solve do not do it.
The motherboard drivers to a certain degree are the same but the updates are usually because of a fault being patched.
You could update them I suppose but don't expect to see any difference.