Are Iori’s other Valor Strikes besides Tsubame Gaeshi (Onefold Path of Light and Tread the Twofold Realm) references to anything?
Koubou Issen, localized as Onefold Path of Light, is an idiom I can't find the etymology for. Its literal calque is "flashing ray of light" and its practical meaning is to change suddenly. The English idiom "In a flash" functions exactly the same way and with the same imagery.
Niga Byakutou, localized as Tread the Twofold Realm, is a quote from Sanshanyi: Simplified Explanation of the Amitayurdhyana Sutra. Its literal calque is "the white path has two rivers" and it refers to the path to reincarnating in paradise. The "two rivers" part refers to a river of fire symbolizing rage and a river of water symbolizing greed. The white path to Nirvana is surrounded by these two. Its description says that if you stay firm in this part while outrunning your pursuers, you'll reach Amitabha's Pure Land, teaching the lesson that even the one most plagued by world desires can cross to enlightenment if they devote themselves to their inner Buddha.