it seems only two people in the world write good articles on this (as well as edaboard correspondents)
The two are Christophe Basso and Ray Ridley
happy googling and you will find out your answers.
C2 is a pole...its for stability as well as noise
I think C1 gives a zero
The TL431 is a pain as its cathode and supply node are the SAME pin.
...so you have to put its operating current into the cathode.
The TL431/opto combo gives an absolutely awful transient response......probably about 2KHz max. if youre lucky.
Is that OK for a Fender guitar amp power supply?...i dont know.