The requirement to know and understand the Catholic faith is not binding on non-Catholics, but, of course, lack of interest in the Catechism is, on some level, a lack of interest in Christianity.
The relevant document regarding the fasting legalities is not the Catechism, by the way. The easiest thing is to ask your priest what to do, or if you suspect that his advice is inaccurate, research some more.
I fast on Friday because I want to express my love of Christ in that simple and direct way. If you had not asked, I would not have a reason to research it further.
I do recommend people of any religion to read the Catechism. Here it is: CATECHISM OF THE CATHOLIC CHURCH. If that is too voluminous, here is a Reader's Digest version: Compendium OF THE CATECHISM OF THE CATHOLIC CHURCH.
I don’t think so. It’s full of doctrines of man. I’ll stick with what God requires of me.