Who's pitching first?

[bsaucer]

Hypothetical question(s): P1 is listed as the starting pitcher in the initial lineup for the visiting team, and bats ninth (No DH). During the top of the first inning, the visiting team puts in a pinch hitter for P1...

1. Is this a legal substitution?
2. May P1 still pitch in the game?

...To continue... P2 pitches in the bottom of the first and loads the bases with nobody out. P3 replaces P2. Without pitching a single pitch, P3 manages to pick off the runners to end the inning. P4 pitches in the second inning and the remainder of the game.

3. Who is the "starting pitcher"?

4. Assuming the visiting team took the lead in the top of the first and maintained the lead for the win, who is the winning pitcher?