In the first season, next to zero. First of all, it takes place in 1946. We don't know exactly when Bucky was found by HYDRA and he certainly wouldn't have gotten all the training/programing needed to be WS that quickly. Second, the showrunners have said that they want this show to be focused around Peggy Carter, so I think that they'll limit the amount of recognizable guest stars early on (the only one that's been mentioned by name so far is Howard Stark). That being said, if the show does well-enough to get more seasons, then maybe they'll open things up more.