I know I need to complete the Assasination Contracts to unlock the pistol swords, but do I have to complete them perfectly? I noticed some of these missions have additional rewards for "stay our of combat", do I need to get those rewards to be able to unlock the swords?
You do not need to "100% perfect" the assassination missions. The requirement for unlocking the pistol swords is simply "complete all assassination missions".
The sub-objectives, IIRC, are simply a means to earn more reward. They may, however, count towards 100% synchronisation.