The diode that you have indicated is called a Flyback or Freewheeling diode and its purpose is to protect the circuit from inductive voltage spikes that will come from the coil when the circuit is opened This diode can be any standard diode similar to 1N40011N4001 as it only has to handle a very small current for a short period of time The capacitor that you have circled is a buffer capacitor that is used to stabilize the power supply When there is a sudden demand for current in the circuit a power supply may drop in voltage briefly and this can cause problems The capacitor provides a means to supply an extra short period boost of current to the circuit I would recommend a 100 uF to a 470 uF capacitor with a voltage rating that is about twice the voltage of your power supply
