(1) Grave worshipping i.e. bowing down to graves ad doing tawaf is unlawful and polytheistic. It is allowed to do isal-e-thawab after reciting Fatiha at graves. Muslims visit graves for doing isal-e-thawab but those committing polytheistic acts like bowing down etc go against the Islamic teachings.
(2) Some Sunnah are muakkada such as two rakah before Fajr, four rakah before Zuhar and two rakah after it, two rakah after Maghrib and two rakah after Isha, it is essential to perform them all, one will be sinful if missed. While, some Sunnah are ghair muakkada like four rakah before Asr, two rakah after the sunnah of Maghrib, and two rakah after two-rakah sunnah of Isha. Performing them is also proved by the Prophet (صلى الله عليه وسلم) but it is not proved to offer them punctually. Therefore, offering is a cause reward but leaving them is not sin.
(b) Niyat is the intention of heart, if you are going to offer any salah and you have the intention in the heart for it e.g. I am going to perform four rakah salah of Zuhr’, it is enough and it is called niyat. But, sometimes one’s heart wanders here and there, so it is possible that one does niyat without having it in the heart, therefore he is asked to do niyat by tongue saying for example: ‘I am going to perform four rakah salah sunnah of Zuhar’ so that the heart is present with the tongue and the niyat is right.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband