H.G.'s point on excessive proliferation (what I call "the tribble effect") is a good one, if a little exaggerated. As a solution, I'd recommend using my suggestion of leaving the new Pawn behind in the space vacated by the Queen. Then, not only does it take at least two turns to make each one, but the player is limited to eight without also moving the King.
As for the double-step question, I'd suggest allowing it only for Pawns spawned in the first two rows, just to avoid confusion (since the "born" Pawns are presumably indistinguishable from the ones the player starts with).
H.G.'s point on excessive proliferation (what I call "the tribble effect") is a good one, if a little exaggerated. As a solution, I'd recommend using my suggestion of leaving the new Pawn behind in the space vacated by the Queen. Then, not only does it take at least two turns to make each one, but the player is limited to eight without also moving the King.
As for the double-step question, I'd suggest allowing it only for Pawns spawned in the first two rows, just to avoid confusion (since the "born" Pawns are presumably indistinguishable from the ones the player starts with).