Just remember if you do ever get another bird that Pepper remains the number one bird meaning he is first to be fed, let out of his cage when you come home, first to be spoken to and such, he will assume the position of flock leader and he must be shown that respect.
When you said he becomes feisty that is the leader coming out in him, he likes Missy but when he has had enough he lets her know but then that is ok.