The primary supply is now 12 volts because when you use a 12 volt relay that winds up being where the load is greatest. Therefore, using a buck converter to make the 5 volts for the rest of the system makes more sense than trying to boost 5 volts to power the relay. That does mean that the voltmeter winds up being powered by the buck converter on the display/logic board, but that seems to be ok.

The switching part for the 12 volt relay is now a self-contained protected MOSFET designed specifically to drive inductive loads like relays. It includes self-protection against coil collapse voltages and short circuits. It's also in a beefier package.