Ruling on invoking blessings on the Prophet aloud and making collective Du`a' after Salah

Q 1: What is the Islamic ruling on the following: Invoking peace and blessings upon the Prophet aloud after the congregational Salah (Prayers), making Du`a' (supplication) collectively after offering Salah, reciting a Hizb (a 60th portion of the Qur'an) collectively, singing in different styles, and praying behind a blind Imam who sometimes makes mistakes in recitation?

A: Firstly, invoking peace and blessing upon the Prophet (peace be upon him) is greatly rewarded and enjoined by Allah (Exalted be He) in the Glorious Qur'an. Additionally, the Prophet (peace be upon him) encourages Muslims to conduct this practice as it entails double reward based on the Prophet's (peace be upon him) Hadith, If anyone invokes blessings on me once, Allah will bless him ten times. Muslims are prescribed to invoke peace and blessings upon the Prophet when his name is mentioned, after reciting Tashahhud (testification recited in the sitting position in the second/last unit of Prayer) in Salah, during delivering Khutbah (sermon) on Friday, marriage, and the like. We know of no proof showing that the Prophet (peace be upon him), the Sahabah (may Allah be pleased with them), or the leading scholars of Salaf (Righteous Predecessors) including Malik, Abu Hanifah, Al-Layth ibn Sa`d, Al-Shafi`y, Al-Awza`y and Ahmad (may Allah be merciful to them) ever invoked peace and blessings upon the Prophet aloud after finishing Salah collectively. The best a Muslim can do is to follow the guidance of the Prophet, the Rightly-Guided Caliphs, and the Sahabah (may Allah be pleased with them). It was authentically reported that the Prophet (peace be upon him) said, Whoever innovates something in this matter of ours that is not part of it, will have it rejected. (Part No. 2; Page No. 526)  Secondly, Du`a' is an act of worship. Yet, it was not authentically reported that the Prophet (peace be upon him), the Rightly-Guided Caliphs, or the rest of the Sahabah (may Allah be pleased with them) made Du`a' collectively after Salah. Based on this, gathering after Salah to make Du`a' collectively counts as Bid`ah. It was authentically reported that the Prophet (peace be upon him) said, Whoever innovates something in this matter of ours that is not part of it, will have it rejected. According to another narration, Whoever does an action which is not in accordance with this matter of ours [Islam], will have it rejected. Thirdly, With regard to reciting the Qur'an collectively, it is unlawful if the people who attend the gathering recite together. This practice is not authentically traced back to the Prophet (peace be upon him) or any of the Sahabah (may Allah be pleased with them). Yet, if someone in the gathering recites and the rest listen to him, or if each one in the gathering recites individually without keeping a collective rhythm, or trying to synchronize with others in the start, end, and pauses made during recitation, there will be nothing wrong with the recitation. It was authentically reported that the Prophet (peace be upon him) said, No group of people gather in one of the Houses of Allah to recite the Book of Allah and study it together without tranquility descending upon them, the angels surrounding them, mercy coming down upon them, and Allah mentioning them to those who are with Him. Narrated by Muslim. It was authentically reported from `Abdullah ibn Mas`ud (may Allah be pleased with him) that he said, The Prophet (peace be upon him) said to me, "Recite (of the Quran) to me." I said, 'Shall I recite it to you although it has been revealed to you?!' He said, 'I like to hear (the Qur'an) from others.' So I recited Surah Al-Nisa' until I reached How (will it be) then, when We bring from each nation a witness and We bring you (O Muhammad صلى الله عليه وسلم) as a witness against these people? Then, he said, "Stop!" Behold, his eyes were shedding tears then.' (Part No. 2; Page No. 527)  Narrated by Al-Bukhari and Muslim. Fourth, Offering a congregational Salah behind a blind Imam is permissible. It might even be better if he is more versed in the Qur'an than any of the people led by him. This is based on the general application of the Hadith of the Prophet (peace be upon him), Whoever is most versed in Allah's Book should act as Imam for the people... If the said Imam makes mistakes in recitation, the Salah will be acceptable if the mistakes involve Lahn (incorrect recitation due to mispronunciation of letters or syntax) that does not change the meaning. However, appointing an Imam who is free from such mistakes is preferred. If the Lahn in Surah Al-Fatihah changes the meaning, the Salah led by this Imam will be Batil (null and void), because of the Lahn not because of his blindness. Examples of Lahn include pronouncing the vowel mark fatha (a) as a kasrah (i) in the word 'Iyyaka' (this will make it a pronoun referring to a female instead of male) or as dammah (u) in the word 'an`amta (this will make it a first person pronoun whereas it is a second person pronoun). If the mistakes are due to poor memorization, appointing another person who has memorized the Qur'an better is recommended.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.