3) Sean Manaea
The role Adrian Houser will play on this Mets team remains to be seen. He has experience both starting games and coming out of the bullpen, making him an ideal swingman candidate. Another free agent who both started games and came out of the bullpen this past season is Sean Manaea, who now doesn't make much sense as a potential Mets target.
Manaea started 10 of the 37 games he appeared in for the Giants this past season, posting a 4.44 ERA in 117.2 innings pitched. He had been a decent mid-rotation starter throughout his Athletics career, but struggled last season in San Diego and wasn't great for a good portion of this season with San Francisco, although he did finish strong with a 3.43 ERA in the second half.
The Mets need as much pitching depth as possible, and that's what Houser provides. He's set to make around $5 million according to Spotrac, and only has one year of team control. Manaea on the other hand, is predicted to earn a two-year deal worth $22 million by MLB Trade Rumors. There's no way of knowing what his contract will be when he signs it, but it will almost certainly be more expensive than Houser's deal.
After the Houser addition, the Mets need to focus on upgrading the top of the rotation. They've got enough back end types of starters. Adding Yamamoto is the dream, but there are several alternatives David Stearns can turn to as well. Manaea no longer makes any sense.