Question :Can we read any surah in Salat Witr or are we prohibited from reading one particular surah?
Answer: You can read any surah in addition to Fatiha
Question: Do we have to read the surah in Salaah in order of the Quran? Like first Surah Falak and then Surah Nas and not reverse?
Answer: You should read in the order of the Quran.
... and Allah knows best.