The Hindu temple seen when Raj takes Howard to visit, is actually the Malibu Hindu Temple, at 1600 Las Virgenes Canyon Road, in Calabasas, CA. (That's about 40 miles West of Pasadena, where the guys live and work.)
Leonard being forbidden to whistle was already mentioned in The Friendship Algorithm (2009) where he demonstrated it to Penny, and immediately got a reprimand from Sheldon ("First warning!").
Title Reference: Refers to Raj's mental state over the success of a space probe mission he worked on.
Leonard mentioning Sheldon's emotional breakdown where he ran away on a train refers to the previous season's finale, The Status Quo Combustion (2014). One of the reasons for that was also because Leonard wanted to live with Penny. His concession to Sheldon that he stay over at Penny only one night a week really isn't that big a change, since they already seem to be doing that for a while.