Add Second processor to ML350e Gen8 v2

Looking to purchase a ML350e Gen8 v2 (749356-S01). I want to add a second processor. From what I understand the PSU needs to be upgraded also. So what i have been told is that I will need the following parts for a second processor.

• QTY 1 – 701841-B21  Xeon Processor E5-2420v2
• QTY 1 -  738661-B21 HP ML350e v2 Redundant Power Supply
• QTY 1 -  503296-B21 PSU Kit

Couple of questions. 

Is only one redundant PSU enough or is two required for two processors?

Is the 460w PSU enough or do I need the 750w psu for two processors?

Does the old PSU stay in the machine with the Redundant Power Supply?

Thanks