Is it permissible for a worshipper to recite two surahs in each rak'ah of a prayer (whether in congregation or individually)?

There is no harm in a worshipper reciting two or three surahs after Al-Fatihah, whether he is an imam or a follower, and whether in obligatory or supererogatory prayers. It is permissible for the imam to do so occasionally to demonstrate its permissibility, provided he does not prolong the prayer for the worshippers. It has been authentically reported that the Prophet, peace and blessings be upon him, recited two surahs after Al-Fatihah in several prayers, and these surahs were called "An-Naza'ir" (the parallels). It is also permissible to recite more than two surahs in a single rak'ah.

As for reciting Surat Al-Ikhlas after every recitation in every rak'ah, this has been authentically reported from one of the Companions and was approved by the Prophet, peace and blessings be upon him, which indicates the permissibility of this act. However, it is not recommended because the Prophet, peace and blessings be upon him, did not do it regularly or consistently.