Since Allah is free from body, shape and space why did He create a Throne and a Footstool?
Arsh and Kursi are part of the Mutashabihat. They are not comparable to human concepts of throne and footstool, there is nothing comparable to Allah, He is beyond our ability to comprehend. Delving in or asking about the Mutashabihat is not good and no one can give you an answer since only Allah knows their meaning, read verse 7 of Surah Aale Imran:
He is the One who has revealed to you the Book (the Qur’ān). Out of it there are verses that are MuHkamāt (of established meaning), which are the principal verses of the Book, and some others are Mutashābihāt (whose definite meanings are unknown). Now those who have perversity in their hearts go after such part of it as is mutashābih, seeking (to create) discord, and searching for its interpretation (that meets their desires), while no one knows its interpretation except Allah; and those well-grounded in knowledge say: “We believe therein; all is from our Lord.” Only the men of understanding observe the advice.