1)
What is the difference between Pasuk 12 and Pasuk 13? When do we apply "ke'Erk'cha kein Yakum" and when do we apply "Veyasaf Chamishis Kesef Erk'cha alav"?
1.
Rashi: Pasuk 12 refers to somebody else who redeems the animal, who pays the value of the animal to Hekdesh, based on the Kohen's evaluation; Whereas Pasuk 13 is referring to the owner of the animal (who has the first right to redeem it, and) who is obligated to add a fifth. 1
1
See Torah Temimah, note 65, who elaborates.
2)
Why does the Torah use the double expression "ve'Im Ga'ol Yig'alenah"?
1.
Sifra: To incorporate a woman and an heir in the Din of adding a fifth when redeeming their property from Hekdesh.
