Well, the answer to the first question is known.
Who the first announcer was is unknown.
Early Voices
We do know one of the earliest PA voices is included in the above photo courtesy of historian Bob Warrington featuring Game 1 of the 1915 World Series between the Boston Red Sox and Phillies at North Philadelphia’s Baker Bowl.
The four men on the right are umpires Bill Klem, Billy Evans, “Silk” O’Loughlin and “Cy” Rigle. On the left, holding a giant megaphone, is the PA announcer, known only by his surname “Smith.