Yes. Only one brake is not good. Although the front is the most important, 2 brakes front/rear are not redundant, I use them both.

Disc/V at the front/rear is fine.

Some people prefer discs because you won't overheat the rim and risk a tube blowout in a looong descent. If that happens in practice I don't know. Some say rim brakes are more serviceable are parts are more common. A disc brake requires tight tolerances between rotor and pad but isn't affected by disaligned wheels.