Answer
(Fatwa: 1243/167=L/1429)
(1-2) Niyah means intending by heart, it is not necessary to utter it by mouth; therefore if a man has the intention of keeping so and so fast while having sahri, then it is also right, but it is better to utter in words. Words regarding the niyah have not been narrated from the Prophet (صلي الله عليه وسلم). For the sake of common people the calendars write niyah in Arabic: بصوم غد نويت من شهر رمضان
It is also right if any person makes intention in his mother tongue in words expressing the intention of keeping fasts of the month of Ramazan:
والسنة أن يتلفظ بها في الشامي اي سنة المشائخ لا النبي صلی الله عليه وسلم لعدم ورود النطق بها عنه (شامي 3:345)
This is the famous dua of Iftar which you have written in No. 3. However, such dua is found in the books of Ahadith, as it mentioned in Abu Dawood:
عن معاذ بن زهرة قال: أن النبي صلی الله عليه وسلم كان اذا أفطر قال: اللهم لك صمت وعلی رزقك أفطرت (مشكاة: 175)
There is another dua as well:
عن ابن عمر قال: كان النبي صلی الله عليه وسلم اذا أفطر قال: ذهب الظمأ وابتلت العروق وثبت الأجر ان شاء الله تعالی (حواله سابق)
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband