Driving 12v SevSeg from Arduino 5v

Using Arduino LEDs and Multiplexing
2

  1. yes, without you will damage your Arduino.

  2. It top switching 12v you need both. If bottom switching you need just an NPN. For example if you have a common anode just connect it to 12 V with the cathode connected to the resistor and then to the collector, emitter to ground and base through a resistor to Arduino output.