You are handsoldering through hole, so you will want a wire diameter that will give you a good amount of solder in a small amount of time. While you want thin wire (.010-.015") for SMT, you want thicker for TH, but I'm not sure of the exact diameter (.025-040?). SAC 305, 2-3% flux so you get good wetting. We use Alpha Telecore Plus or Kester 275, maybe others. Just a note, the lead-free solder is not lead-free. It usually has a Pb content betwee 300 and 700 ppm.