Is the Hadith, "The best of you is he who learns knowledge and teaches it," authentic, and is there a Hadith that praises those who supplicate in mosques, raising their voices in collective supplication?

The hadith mentioned in the question, "The best among you is he who learns the Qur'an and teaches it," is authentic and was narrated by Al-Bukhari. Among the soundest narrations regarding the virtue of collective remembrance (dhikr) and supplication (du'a) in the mosque is what Abu Hurairah (may Allah be pleased with him) narrated, that the Prophet (peace be upon him) said: "Allah has angels who roam the roads, seeking the people of remembrance. When they find people remembering Allah, they call out to one another: 'Come to your need!' So they encircle them with their wings up to the lower heaven. Their Lord asks them, though He knows best: 'What are My servants saying?' They reply: 'They are glorifying You (tasbeeh), magnifying You (takbeer), praising You (tahmeed), and extolling You (tamjeed).' He asks: 'Have they seen Me?' They say: 'No, by Allah, they have not seen You.' He asks: 'How would it be if they had seen Me?' They reply: 'If they had seen You, they would have been even more intense in their worship, extolling, and glorifying You.' He asks: 'What are they asking for?' They reply: 'They are asking You for Paradise.' He asks: 'Have they seen it?' They say: 'No, by Allah, they have not seen it.' He asks: 'How would it be if they had seen it?' They reply: 'If they had seen it, they would have been even more eager for it, seeking it more ardently, and desiring it more intensely.' He asks: 'From what are they seeking refuge?' They reply: 'From the Fire.' He asks: 'Have they seen it?' They say: 'No, by Allah, they have not seen it.' He asks: 'How would it be if they had seen it?' They reply: 'If they had seen it, they would have been even more fervent in fleeing from it and fearing it.' He then says: 'I bear witness to you that I have forgiven them.' Then an angel says: 'Among them is so-and-so, who is not one of them; he only came for a need.' He says: 'They are the companions; their companion will not be miserable.'" As for the supplication in the specific form mentioned in the question, no hadith has been reported concerning it.