I think going by the previous episodes Red John has to be somebody who's
- male, probably older: his voice is male and it was mentioned that he's a little shorter than Jane
- part of the CBI since he's always aware of what's happening and is able to hack into the system every now and then...
- someone with many followers (also in the CBI and FBI), probably a great hypnotist (incognito) as well
- someone with a major superiority complex... a father figure with a soft voice (Stiles voice is too powerful) and in a high position
- someone who knows what Jane and Lisbon share... why else would he ask for Lisbon's body in season 4 finale...
- someone who lives alone without family so he can go unnoticed
- someone whom Jane knows since he prefers to wear a mask during their encounter

Why did Virgil Minelli leave after Boscos murder... to go fishing? I doubt if a CBI chief could really relax or retire early after a highly geared-up life full of action... seems strange... when the lady who killed Bosco was being questioned Minelli was also present there and seemed quite nervous.. he probably poisoned her and was hoping she'd die soon. He pretends to be very straightforward and resentful of Jane's methods but I think he's just playing games with him and is in league with Bret Stiles. He actually tries to act stupid most of the time... I even think he faked his voice every now and then when he was CBI chief.