#1
Someone once told me he did. But I've looked up some live videos and they all look like he's playing 6 strings. Yet they tune down to like B or Bb for many songs. So does he use 7 strings or not?
#2
he has been know to use 7 strings occasionally, primarily he uses 6, i`m sure the was a JP7 sig guitar.
#4
Yes and he has his own signature 7string model of his 6string music man
Guitar - Music Man John Petrucci X

Amp - Ronald cube 60, willing be getting a Mark V soon