How does the fact that the tributes are always on camera affect their behavior from the time they are chosen? Does it make it easier or harder for them to accept their fate? How are the “career tributes” different from the others?

You have a few questions here. I think cameras always mean that the tributes must entertain to get sponsor points. This means added pressure on top of trying to stay alive. No, cameras do not make it easier to die. The cameras just add more exploitation to their already tragic demise. The careers have spent their entire lives training for the games. They had more money and backing behind them.