The title echoes a line from the 1890 Sir Arthur Conan Doyle novel, "The Sign of the Four," in which Sherlock describes his cocaine injection as a seven-per-cent solution. The "One Percent" comes from the movement that campaigns against rich people.
Romulus and Remus were characters from Roman Mythology, they were brothers who were mortal enemies and tried to kill each other. Eventually Remus was killed by Romulus.
Holmes tells Watson that Lestrade's password is the last time Spurs won the FA Cup. At the time of broadcast, the last time that happened was on May 18th, 1991, when they beat Nottingham Forest 2-1.