I would only caution (not on this point, because I believe it is abundantly clear) about Passover traditions in general that it may not be safe to assume that rabbinic custom is the same as Second Temple practice.
From my reading it appears that there were competing customs among the various groups (Pharisees and Sadducees, for example). Rabbinic practice stems from the Pharisees and we have no idea exactly how Jesus and his followers would have celebrated the Passover other than from what the gospels tell us; thus we cannot say how closely the Last Supper would have conformed to later rabbinic practice.
This is especially important in that rabbinic practice had to be modified for two reasons: The Temple had been destroyed, essentially ending the sacrifices that were central to the Passover, and there may have been alterations in the ceremony introduced to distinguish it from the Lord's Supper, which appropriates the Passover and transforms it into something entirely different. Hillel the Younger almost certainly made modifications to the ceremony, but in the end there is no way to know exactly how different rabbinic custom is and what Jesus may have followed.
From my reading it appears that there were competing customs among the various groups (Pharisees and Sadducees, for example). Rabbinic practice stems from the Pharisees and we have no idea exactly how Jesus and his followers would have celebrated the Passover other than from what the gospels tell us; thus we cannot say how closely the Last Supper would have conformed to later rabbinic practice.
This is especially important in that rabbinic practice had to be modified for two reasons: The Temple had been destroyed, essentially ending the sacrifices that were central to the Passover, and there may have been alterations in the ceremony introduced to distinguish it from the Lord's Supper, which appropriates the Passover and transforms it into something entirely different. Hillel the Younger almost certainly made modifications to the ceremony, but in the end there is no way to know exactly how different rabbinic custom is and what Jesus may have followed.