If a Muslim does his best to figure out the direction of the Qiblah, and then prays but finds out later that he was mistaken, his prayer would still be valid.

The time for Tarawih prayer lasts from after `Isha until dawn comes, so it is valid to perform this prayer at any time during this period.

There is no sahih hadith concerning the virtue of the night of the fifteenth of Sha’ban. With regard to Allah’s descending on the 15th night of Sha’ban, there are hadith which are weak, but the reports that He descends every night are proven and sahih, so the night of the fifteenth of Sha’ban is included in that. For more, please see the detailed answer.

What is narrated about praying, fasting and worshipping on the 15th of Sha’ban is fabricated. So it is not permissible to follow such hadiths or to act upon them, whether that is in doing righteous deeds or otherwise. For more, please see the detailed answer.

The correct opinion is that Salatul Tasbih is not sunnah (from the prophetic teachings), and that the hadith about it is weak for several reasons which are detailed below.