Money's going to be important in 2016. Pending free agents: Aramis Ramirez (retiring), A.J. Burnett (retiring), Joakim Soria, J.A. Happ, Antonio Bastardo, Corey Hart, Sean Rodriguez, Joe Blanton.
2016 payroll obligations: The Pirates have $50.6 million committed for next season according to Cot's Baseball Contracts, though they do have several significant arbitration cases, including Walker, Cervelli, Alvarez, Melancon, Watson, Locke and Jared Hughes. That $50.6 million is really more like $90 million after arbitration raises.
Jeemie, here's my opinion, FWIW to you. Say good bye to ARAM, AJ, Hart, and Soria. Kang/J-Hay/Mercer/Walker make ARAM expendable even if he wanted to return, which he says he doesn't. AJ is adamant about going, and his arm falling off for 2 months along with his age make him expendable, to say nothing of whoever will be the latest Sea-Rage reclamation signing. Do I need to discuss Corey Hart? IMHO, Soria will get a better offer somewhere else because some teams may see him as a poor-man's closer.
That leaves for consideration in no particular order from your list the following: Happy, Bastard, Serpico, and Blanton.
I expect Bastard to get an offer because he's a veteran lefty who can complement/spell Watson.
I would expect Blanton to get a take it or leave it offer, which Blanton probably will leave.
Serpico offers versatility in the field but only at the right price. If he goes he goes.
I expect the team to make a run @ Happy to at least give the impression they tried to keep Happy happy. Happy presents a nice lefty option to replace Nibbles and to join Frankie as another lefty on the starting rotation. Happy would present the Cardinals some problems much like Frankie does. I'm not sure the Pirates would dare offer Happy a 1-year tender similar to what they offered Martin or Frankie last year because Happy might call their bluff and another draft pick is only worth so much.

It would be nice if they knew in advance if he'd accept or decline it. They might even ask him to reject it officially and then sign a longer term deal to get the extra draft pick?
Cervelli, Melancon, Watson, and Huey will return. That leaves Alvarez, Walker, and Locke.
I like the idea of cutting teacher's pet (CMo), but I won't hold my breath waiting for that.
Locke will probably stay simply because he's a lefty who can eat innings until the latest YOC (Years of Control) pitcher arrives.
I don't know if Alvarez or Walker will return. For some reason I expect one to stay and one to go just to address your concerns about arbitration $.
If Walker & a minor league prospect were traded for a legitimate left-handed first baseman that would open the way to jettison Pedro as well.