1)
Why does it say again "Ein Melech b'Yisrael"? Its already said so twice (17:6, 18:1)!
1.
Malbim: Also Pilegesh b'Giv'ah was due to the lack of a king to punish sinners. When there is a king, people do not kill each other like moths consuming a garment.
2)
What is the status of a Pilegesh?
1.
Refer to 8:31:1:1,2 and the notes there.
3)
Is it permitted to have a Pilegesh?
1.
Refer to 8:31:2:1,2 and the notes there.