The first part of the movie was pure nonsense and really killed it for me. I was too distracted by the absurdity of the situation to pay any attention to anything those ninjas said before dying, so I was lost pretty early in the story.
If the idea was to test his strength, then a duel with the strongest of the five would have sufficed (it also wouldn't need to be to the death, but in this series that's unavoidable). The poison was completely out of place as well: they wanted him to kill a man, not infiltrate a court, so what would that "test" accomplish?
The worst part though, was waiting until they were mortally wounded to explain to him the details of the mission. Considering that the majority of his opponents die pretty much instantly, he could have easily slain all of them, never hearing a word about their mission. That makes me wonder, if that's a common strategy, how many of his previous fights could have simply been misfired attempts at hiring him. How many plots could he have been sidestepping all this time, unbeknown to both him and the audience?
I think that there are two reasons for the bizarre way of hiring Ogami by the five fighters challenging him.
1. To test his abilities. If they can kill him, he has no way of being able to kill the abbot.
2. To die for the cause. By giving their lives, the five fighters show that it is really important to have the abbot killed. Even though he is (considered) a Buddha and really not a person one would want to kill (ha he not also been the evil head of a ninja clan that is)
Itto avoids killing them instantly so that he can listen to them talk before they die. He does not decapitate them for instance. Besides, there are many occasions in the movies where he kills people slowly, sometimes because they want to see his technique in action and sometimes because it just happens. He cuts of the limbs of all those ninjas in number 4 and it's almost monty pythonesque when the last one tries to bite Ogami, only to be killed of course.
I don't know why the woman commited seppuku at the beach, if she was the mother of the prince. That does not make any sense to me. Maybe she lost face because she hadn't told about the fake prince, a fact she must have known for a long time. When that became public, people would know her son had been hidden away and