Answer
(Fatwa: 893/707=L/1430)
One should not respond the azan called before khutbah of Jumu’ah, one only can respond in his heart:
وینبغي أن لا یجیب بلسانہ اتفاقاً في الأذان بین یدي الخطیب (الدر المختار مع الشامي 2:70)
(2) The rulings mentioned in the question from a-c are alright.
(3) Saying Allahu Akbar for reciting qunoot is wajib according to one opinion, but the preferred opinion is that it is not wajib: وینبغي ترجیح عدم الوجوب لأنہ الأصل ولا دلیل علیہ (الشامي 2:163)
It is not necessary in Witr to recite particular dua (اللھم انا نستعینک), rather it is sunnah, therefore if someone recites ربنا آتنا فی الدنیا حسنۃ الخ instead, he will not have to perform sajdah sahv (remedial sajdah). But, one who knows the qunoot by heart, he should not recite ربنا آتنا۔۔. Yes, one who cannot recite the qunoot he can recite ربنا آتنا.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband