Is the worshiper required to say the opening Takbir (Takbirat al-Ihram) after standing firm, and does moving during the Takbir affect his prayer and the prayer of those following him?

One must stand upright for the opening takbir (Allahu Akbar) in a fard (obligatory) prayer, if one is able. It is not permissible for the worshipper to begin the prayer while bowing. As for walking during the opening takbir, it is not appropriate, because even if one fears missing the takbir if they do not hasten, they are not encouraged to hasten; rather, they should walk with tranquility and dignity. However, this walking does not affect the validity of the ihram (entering into prayer) or the validity of the prayer, as it is considered a minor action during prayer.