Qiraat

Q: Can Surah Ikhlass be recited in the first rakaat and either Surah Falaq or Surah Naas in the second rakaat?

Q: What about specifically misprounincing the letter ذ as ز , ظ or the letter ث as س , ص ? For non-arabs the letters ذ , ظ , and ث are quote difficult to pronounce since these letters are prounounced with a lisp i.e bringing the tongue between the upper and lower teeth when pronouncing it. So the non-arabs because they are not used to the lisp sound read the same representative lettersound without the lisp. In such case is the salaah invalid either intentionally or unintentionally?

Q: Letters which have similar sounds like: ذ , ز , ظ does mixing up between them nullify the salaah? Also ت , ط and also ث , س , ص and also د , ض and also ح , ه and also ا , ع also ق, ك does mixing up between these letters nullify the salaah? I read that there a different views, but what is view that is to be taken ? And what did the majority say?

Q:

1. Is it imperative to read diff rent surats each day in the five salaats? Would salaat be valid if one continuously recites the same surats only.  For example, in the Maghrib salaat each day, one habitually recites sura Falaq in the first rakaat and sura Naas in the second rakaat. 
2. Can Ayatul Kursi be recited in place of a sura in salaat or is it necessary to add at least two ayaats before or after ayaatul Kursi?

Q: Reading salaat behind Imam in jamaat, in the last two rakaat what should one recite, according to Shafii Maslak?

Q: I have a question regarding Salaah. For eg. In Esha Salaah there are four rakaat's, in which two are audible and two are silent. What should we do in the last two rakaats?