I see 3 solid starting talents there assuming Robles to be ready in 2019, and 2 4th OF types in MAT and Goodwin. I'm not sure what excess we'd be trading from if Harper walks. MAT/Goodwin aren't really good enough to start ideally, and neither is fetching a solid SP.
Trade Robles
Soto/Taylor/Eaton, all under team control through 2020, with Goodwin and Stevenson filling in as extra outfielders.
Robles gets you Gio or Murphy's replacement.