Please can you advise why it is that only in FARD salaat the third/fourth rakaat you dont recite any surah from the quran?

2) I was recently informed by a friend that you only recite Surah Iklyas(or any surah from the koran) in the first two rakaat of a FARD salaat and for the third/fourth rakaat surah fathiah is all you need to recite. I have always recited Surah Iklyas in my FARD salaat in the third/fourth rakaat as I was not aware of this. Please can you advise if my salaat will have been accepted? 3) I want to make up for the prayers I never used to pray, please can you advise if I only need to pray the fard for each salaat I ever missed. e.g Dhur salaat is 4 sunnat, 4 fard, 2 sunnat, 2 nafl, however do I only need to pray 4 fard of Dhur salaat when doing Qadhaa. I assume for Isha I need to also pray 3 Witr as well as 4 fard.