You siad, "When Peter spoke of 'the Holy One and the Just' [Acts 3:14], had Peter not already seen Jesus in person?"
Yes. But what is your point? Are you implying that Peter saw Jesus' Holiness? Nothing like that is stated anywhere. Jesus is the Holy One and Just, and that is Who Peter saw. Nothing more.
witness manifest holiness with one's own eyes.
That Peter spoke of the Holy One and the Just, Whom Peter had seen, is entirely consistent with the notion that Peter had witnessed [Jesus'] manifest holiness with his own eyes.