I hope I don't take too long. Before I start playing GM, I would like to clarify what I see as the team's biggest needs:
1. An impactful Center Fielder
2. A true leadoff hitter with an OBP higher than .340
3. A good starting Catcher
4. At least 2 HR threats: Players who can hit 20+ HRs in 400 ABs.
5. Any combination of the above would be ideal.
Also as you may know, the Marlins' FO already said they will "spend some money" on the FA market this winter, a statement I hardly believe. There are great opportunities to sign players this winter, but I don't see yet signing any of the top ten for 5+years / 100+ MUSD. Second or third tier free agents seems more realistic as they hope Jesús Sánchez and Lewin Díaz keep developing into regular players. Not to mention that the Marlins might have to overpay to attract a targeted Free Agent, given the small market and not-so-sure contending team around the corner. The only player I realistically think they can sign this winter is Starling Marte, only if they offer him a respectful (and well-deserved) 3 years/45+ MMUSD. Time will tell. Prove me wrong, Kim Ng.
That been said, it is fair to say that it should be easier to get players via trade. With a plethora of SPs capable to perform at the highest level, a strong farm system and a bunch of teams under rebuilding mode, why not make the move now? So here I am pretending I can make decisions. I use Baseball Trave Values (BTV) as the only tool I have to make it somehow logical. Let's get started:
1. Cedric Mullins (BTV: 63.9) for Sixto Sánchez (52.5), Jerar Encarnación (6.3), Braxton Garrett (3.7) and Connor Scott (2.1): A little overpay here to make it happen. Makes sense because the Fish get a high OBP CF, a proven leadoff hitter with power and speed, excellent defense and 3 years of team control. Giving 4 prospects in return? Well, Mullins is a top 20 (maybe a top 10) player in the game, so it should cost a lot. Sixto can cause immediate impact in Camden Yards and Braxton will have a better chance there rather than here. Another potential CFs to trade for are Reynolds (PIT, 82.4 - too expensive), K. Marté (ARI, 40.8) and Buxton (MIN, 19.8).
2. Willson Contreras (11.5) for Garret Cooper (9.2), Jose Devers (4.5) and Alex Jackson (0.2): It looks like another overpay, but I don't think Cooper is worth that much, even though we know he can smash the ball when healthy, which is the problem. The cubbies just started a rebuild and both Devers and Jackson can be relevant for the process. Contreras' value should be at its lowest right now. Other options: Garver (MIN, 18.1) and Stallings (PIT, 8.0)
3. Teoscar Hernánadez (32.0) for Jesús Luzardo (17.8), Nasim Núnez (8.4) and Dylan Floro (7.6): This is a trade that the Marlins will probably say no, but makes sense to me because the Blue Jays need pitching now. They are the team with the highest OPS in the majors and might have to sacrifice some of that pop for some arms. Floro has been great with the Marlins and Luzardo looked promising in his last 3-4 starts. Hernandez has been an above average bat for 4 seasons, being All Star-caliber during the last 2.
I am not saying they have to make all those trades, but at least one of them will open a window for bringing a FA, sending the correct message of contending. Despite my favorite trade would be Mullins, bringing Contreras and Marté makes a solid starting lineup.
Marlins being Marlins: Means, solid options without breaking the piggy bank. This section refers to players that are not stars, but worth to take a look. These players won't make us immediate contenders, but with a good season, can definitely put the Marlins in a 75+ wins season: Myles Straw, Tony Kemp, Jeimer Candelario, Ian Happ, Trent Grisham and Hunter Renfroe. Have a look at their stats and see my point.