How many Rak'ahs are there in the Tarawih prayer? And is it permissible for the Imam to begin the Tarawih prayer in the mosque before the first Imam finishes Witr, or to pray a Sunnah prayer after Asr prayer having already led the congregation?

Repeating the congregational prayer in the same mosque is disliked by the majority of scholars if the mosque has a regular imam, due to the dissension it may cause among hearts, unless it is with the imam's permission. As for mosques in markets and the like, or a mosque that does not have an imam, repeating the congregational prayer in them is not disliked. The Hanbalis, however, hold that repeating the congregational prayer is not disliked at all.

For those who enter the mosque while the imam is praying Tarawih: If the imam is praying Witr, they should wait until he finishes and then pray in congregation. This applies if their delay was due to a valid excuse. However, if the delay was due to a disagreement with the regular imam, it is disliked for them to establish a second congregation, and it is better for them to pray individually, because Muslim unity is obligatory, while congregational prayer in Tarawih is a Sunnah.