Method of Salaah

Q: The is a hadith which states the recitation of ayatul kursi after every fardh salah. I want to know does it mean immediatly after fardh or after sunnat?

Q: If in "Ihdeenas-Siratal-Mustaqeem", I recited dee with a daad mistakenly instead of daal does this invalidate the namaz? I don't know for sure if I done it, but it seems likely so should I repeat the namaz or is it an acceptable mistake? I didn't repeat it afterwards.

Q:During tashahhud one says "..as salaamu alayna ayyuhan nabiyyu" instead of "..as salaamu alayka ayyun nabiyyu". Does this mistake invalidate salaah?

Q: Is it sunnat to join your own ankles in ruku and sajdah?

Q: In Kitaab al-Asl of Imaam Muhammad it states that according to Abu Hanifa the imaam should not say "Rabbanaa lakal hamd". But in the same book Imaam Muhammad ask Abu Hanifa whether the Imaam should recite basmalah, amin and Allaahumma rabbanaa lakal hamd silenty and Abu Hanifa says yes. Why this contradiction?

Q: I have a problem reciting a certain part of the Tahiyyaat in Tashahhud. The part is: "...wa alaa ibadillaah'is salihin.." I have trouble pronouncing the last letter "n" out. Is it also permissible to read that part as: "...wa alaa ibaadillaah as salihin.." ? Thus "ibaadillaah" and "as" seperately, instead of connected as "ibaadillaah`is"?

Q: Assuming in the first rakaat of witr, one recites Surah Lahab and Surah Ikhlaas in the second rakaat. Is it necessary to make sajda sahu as only Surah Falak or Surah Naas can be recited in the third rakaat but these Surahs are longer than Surah Ikhlaas. Likewise, in any other namaaz, if one recited a Surah in the second rakaat that is slightly or much longer than the surah recited in the first rakaat, what is the ruling?

Q: Is dua after Salaah and facing the congregation a sunnah? Please elaborate.

Q: In Nizamuddin markaz we have seen that the Imam saheb does not make dua after salah with congregation and we make dua individually but in other masaajid the imam makes very short dua with congregation. Which one is sunnat?

Q: Is it adviseable to ask any dua in salaah?