I think that's probably how it's going to go too. Looks more likely the bat may come via trade, and SP via FA.
Next season we will have a very deep farm at the AAA/AA levels with many guys knocking on the door with essentially no clear holes in terms of positions. Given what we have in the farm upper levels and on the MLB team, I think 1B is the weakest position, followed by 3B. Shaw is a better prospect than Mervis, and I'm not sure if they'd want to block Shaw at 3B longterm on a trade, and he'll move quickly through the minors (should start the year at AA), and he could be up the 2nd half of 2025 barring injury.
Alonso makes the most likely big hitter acquisition IMO. They have more quality options at DH next year and on the farm longterm than at 1B or 3B. Bellinger fills short-term needs, but not longterm ones, and putting him at 1B longterm seems like a waste, and I think he did overachieve a bit last year and will regress somewhat so not interested in an overpay there.
Longterm I do believe they'd have the payroll room to also sign one of Soto or Ohtani, but i'm not sure they'd want to go over the cap the next year or 2 to do it, or sign the massive deals needed. You gotta think Soto is going to sign for 13+ years.