Why does it say "va'Yifros Osah Lefanai"?
Malbim: Initially it was rolled up. I.e. the Nevu'ah came to him in a way that he will understand it and know it - unlike "va'Tehi Lachem Chazus ha'Kol k'Divrei ha'Sefer he'Chasum Asher Yitenu Oso El Yode'a Sefer?" (Yeshayah 29:11).
What is the significance of being written on front and in back?
Rashi citing Targum Yonasan: What was from the beginning, and what will be in the end.
Malbim: It has revealed and hidden [content].
Why does it say "v'Chasuv Eleha"?
Radak: It is as if it says Aleha (on it).
What are "Kinim va'Hegeh va'Hi"?
Rashi: They are, respectively, punishments of Tzadikim in this world, their reward, over which they will sing in the world to come, and the wailing of Resha'im in the world to come.
Radak: They are all expressions of lamenting and eulogy. They were about Yisrael.
Malbim: They are punishments for those who rebel against His Mitzvos and do not heed His words.