Klentak isn't signing Darvish, Arrieta or Tanaka.
I'm convinced their timetable is 2020 to ???
So they'll judge FA by two considerations
1) will they be at least #3 starters after 2020 at a reasonable cost
2) or can they be flipped for assets the next couple years
Big long-term contracts make most FA pitchers untradeable in their out years (unless you're talking an elite pitcher like Verlander).
I do see a veteran SP to buy time for the young arms to develop, but right now I think Klentak hasn't given up on the stable:
Pivetta, Eickhoff, Velasquez, Lively, Thompson, Eflin,
and he'll be watching Eshelman, Anderson, Taveras, Kilome, El Garcia, Irvin, Waguespack, Viza closely.
When they give up on a young starter, it'll be obvious, he'll either be moved to the bullpen (Pinto) or traded.
Nola is their #1, he's better than anyone they can sign or conceivably trade for.
They need to develop two more solid starters over the next two years, the back of the rotation can be filled with guys like Eickhoff.
My bet is on Pivetta and Eflin, with Anderson and Irvin as outside shots.
Best bets to move to the pen, Velasquez and Kilome.
The younger pitchers are too far away, including Sixto and Romero, to affect plans for the next couple years, they won't impact decisions until they get to Reading and show they are potential ML starters there. Even the best are wild cards, they have to start 26 games for a couple seasons at Clearwater and above before they become serious future options.