Is it considered showing off (riya') for a person to review or memorize the Noble Qur’an with the intention of leading people in prayer, knowing that they did not have this intention before starting to lead the prayer, and does this affect the acceptance of their prayer?

Do not abandon leading the people in prayer, for this is a door to goodness. Strive to strengthen your relationship with the Qur’an through memorization and revision, and seek Allah’s help. Do not abandon righteous deeds, and strive to memorize new portions, revise what you have already memorized, and achieve sincerity. You are not a dissembler as long as you intend nothing but to please Allah. Beware of abandoning righteous deeds out of fear of showing off, for this is one of the pitfalls of Satan.