Nawaafil

Q: Kindly advise me which are some of the best Surah's or Ayaat to be recited during Salaatul Haajat?

Q:

1. Could you please provide a hadith with translation  which proves that Prophet Sallalahu alaihe wasalaam recited durood and duaa in the first Qaidah of sunnat e ghair muakkadah salaah &  Sana in the third rakaah of sunnat e ghair muakkadah salaah as what the Fuqaha mention that the above method  is afdhal?
2. Is there a hadith which proves that Prophet Sallalahu alaihe wasalaam didn't recite durood and duaa in the first Qaidah of sunnat e ghair muakkadah salaah &  Sana in the third rakaah of sunnat e ghair muakkadah salaah?

Q: In a four rakaat sunnah ghayr muakkad salaah or a four rakaat nafila prayed with one taslim, if one reads in the first tashahhud after the durood ibrahimiyyah a masnoon dua does this entail sajdah sahw? Or is this permissible?

Q: Do nafil prayers make up deficient fard prayers? Like one missed a pillar of fard salaah unknowingly, or does missing a pillar unknowingly not get one accounted on that?

Q: Is it permissible to pray Salaatul Hajaat on behalf of another person and pray to Allah to ease his difficulties?

Q: Great virtues are mentioned in the Ahadith for praying 4 rakaats after Zuhr and Isha.

Should one perform these apart from the confirmed 2 rakaats sunnah that are prayed after Zuhr and Isha i.e. first 2 rakaats and then 4 rakaats? And these 4 rakaats should they be prayed with one taslim or 2 by 2 rakaats?

Q: Praying four rakaats after the fard of salaat Esha is mentioned in Ahaadith. Its mentioned that the virtue is that one will gain reward as having prayed these four rakaats on Laylat al Qadr. There are both Marfu and Mawquf reports regarding this. Should this be prayed after the 2 rakat sunnah muakkadah as adding 2 rakaats seperately or adding 4 rakaats either seperately or in two sets? 

I read in Qutul al Quluub that Ibn Masud (RA) did not like to pray after the Fard a same amount of Nafila rakaats, they would pray Isha and thereafter 2 rakaats and thereafter 4 rakaats. Is this true?

In Musannaf Ibn Abi Shayba 2/206 there is a report from Umar (RA) that he did not like to pray after Jumuah the same amount of nafil i.e. 2 rakaat. What Ibn Masud (RA) would do, is that 2 rakaats and thereafter 4 rakaats with one taslim?

Q: Is there a limit of how many rakaats of nafl a person can pray with one salam example is it permissible to pray 12 rakaats of nafl with one salam? 

Q: Can you tell me what's the procedure for the salat "hajat”? And what's the purpose of this namaz?

Q: I know that it is a sunnah to read the last 2 nafl of esha salah seated. Should one always do this, or should it be done occasionally only? Does this apply to the nawafil of dhuhr and maghrib as well?