The last ten nights of Ramadan begin from the night before the twenty first day, whether the month is thirty days or is twenty-nine days. The odd-numbered nights of the last ten of Ramadan are the nights before the twenty-first, twenty-third, twenty-fifth, twenty-seventh and twenty-ninth (day).

Praying Tahajjud with 11 or 12 Rak`ahs, reciting Surat Al-Ikhlas 12 times in the first Rak`ah, then reducing the number of times it is recited in each Rak`ah until you recite it just once in the final Rak`ah is an innovation and is contrary to the Sunnah.

Some scholars suggest that if an odd-numbered night coincides with a Friday night in Ramadan, it is more likely to be Laylat Al-Qadr. However, there is no clear Hadith supporting this view. Authentic reports indicate that Laylat Al-Qadr falls within the last ten nights of Ramadan, with odd nights being more probable. The best approach is to seek it on all ten nights, following the Sunnah of the Prophet.

-The Prophet recommended saying “Subhan Al-Malik Al-Quddus” three times after Witr, raising the voice on the third time. -There is no evidence for reciting this Dhikr between the Rak`ahs of Tarawih. -Adhering to the Sunnah in worship is obligatory, and collective recitation of Dhikr—when unsupported by authentic evidence—must be avoided

If you pray Tarawih in one mosque, then you find another mosque where prayers are still going on, and you go and pray with the people, there is nothing wrong with you doing that, but you should not pray Witr twice.

A woman may pray Tarawih at home according to whatever she is able to do, paying attention to the Sunnah as much as possible. For more, please see the detailed answer.