2) Buck Showalter
Buck Showalter is not a manager the Padres have been publicly linked to, and hopefully it'll stay that way. He's a historically great manager who has a shot to make it to the Hall of Fame one day, but he's just not the right fit for this Padres team for a couple of reasons.
First, Showalter reportedly had disagreements with the front office during his time with the Mets. They'd want him to play certain guys because of certain analytics, and Showalter was not a fan of Billy Eppler and the front office telling him what to do. I'm no expert, but going from one guy who did not mesh well with the front office to another with that same history wouldn't be the wisest thing.
Obviously there's no telling whether Showalter and Preller would have any issues until the two actually start working together, but the move would just feel very lateral if the Padres decided to bring Showalter in.
Another reason for the Padres to not consider Buck is the fact that he just hasn't won enough when it matters. He's had great regular season success, but Showalter has gone just 10-16 in his postseason career. Showalter has 22 years of managerial experience and has yet to win a single pennant, let alone a World Series. Again, obviously not all his fault, but he's certainly played a role. Just ask Zack Britton.