The rule that Pawns cannot be dropped on files already containing a Pawn is completely pointless with chess-like pawns. In Shogi this rule is necessary, because Pawns capture straight ahead, and it would be very advantageous to persistently drop Pawns protected by other Pawns, so stick a deadly and unassailable thorn into the opponent's defense line. With chess-like Pawns you could do the same thing, by dropping the Pawns diagonally in front of each other. Your rule does not prevent that. You should forbid dropping a Pawn diagonally in front of another Pawn instead.
The rule that Pawns cannot be dropped on files already containing a Pawn is completely pointless with chess-like pawns. In Shogi this rule is necessary, because Pawns capture straight ahead, and it would be very advantageous to persistently drop Pawns protected by other Pawns, so stick a deadly and unassailable thorn into the opponent's defense line. With chess-like Pawns you could do the same thing, by dropping the Pawns diagonally in front of each other. Your rule does not prevent that. You should forbid dropping a Pawn diagonally in front of another Pawn instead.