Is it sufficient to recite Surat Al-Mulk and the two Zahrawain (Surat Al-Baqarah and Surat Aal-Imran) once, or must they be recited daily for the mentioned benefits in the hadiths to be realized?

Reciting Surah Al-Mulk every night prevents the torment of the grave. As for "Al-Zahrawan" (Al-Baqarah and Al 'Imran), they will intercede for their reciter on the Day of Resurrection. The virtue of reciting these surahs is for those who regularly recite them, ponder their meanings, and act upon what is in them, not for someone who recites them only once.