O'Hoppe might be more valuable over his career, but Marsh provided years of immediate value, and as you point out, is young enough to have upside left.
Marsh and a RH (Wilson, Kemp later in the season?), Rojas (until Crawford is ready to push him).
Castellanos is overpaid because he's such a liability as a fielder, really should be the DH.
I'm not sold that OF is a priority with Crawford, Ricones and Kemp in AAA (Kemp can play IF and OF).
If you have limited resources, I'd focus on a 5th SP for depth and the bullpen.
Worst thing would be spend big money on 5 year deal for 30+ FA and block cheap prospects.