Should the congregant remain silent in the silent prayer after completing the recitation of Al-Fatihah and a surah in the first two rak'ahs, and Al-Fatihah in the last two, and if not, what should he recite?

The Sunnah for a worshipper in a silent prayer is to recite Al-Fatihah and what is easy from the Qur'an in the first two rak'ahs. It is permissible for him to recite more than one surah after Al-Fatihah in the first two rak'ahs. As for the last two rak'ahs, the default is to limit oneself to Al-Fatihah therein, but it is sometimes permissible to recite another surah after Al-Fatihah in them, especially if the worshipper finishes reciting and the Imam has not yet bowed.