It's a lot to ask, but I see Travis d'Arnaud, Lucas Duda and the bullpen as this team's road to success. I trust the infield and I have little worry about the starting rotation, especially with Zack Wheeler on deck. I have faith they'll meet expectations.
Duda just needs to strike out a little less and put more balls in the air. This, plus a year under his belt, and being more comfortable in the field, should let him hit at least 20 home runs with a .350 OBP. However, if he can accelerate that growth and put 30 balls over the fence, it changes the entire lineup.
Similarly, d'Arnaud doesn't need to rise up and win Rookie of the Year... although that would be awesome. Instead, if he simply hits .240, 10 to 15 home runs and knocks in 50 or so runs, in about 400 at bats, he'll double production at catcher from what this team had a year ago.
The Mets scored just 650 runs last season. However, meaningful contributions from Duda and d'Arnaud should tack on enough runs to bump the team's offense to around the middle of the pack in the National League, or right where the Braves, Reds, Phillies and Giants were last season (670 to 700 runs scored). It's not that far away. Also, in this scenario, the mystery of right and center field is significantly less important and any contributions would be an added bonus.
Lastly, the bullpen will either be really good or really bad. That's baseball these days. There doesn't seem to be a third option. I don't care who you are, what you spend or what you did last season, it's a total crapshoot this year. And, for better or worse, the Mets have a lot of crapshoots in camp, from Brandon Lyon to Pedro Feliciano to Greg Burke, not to mention Jeurys Familia, Bobby Parnell, Josh Edgin and others.