The number on Tetch's Arkham uniform is C-106, in Alice in Wonderland the Mad Hatters hat has the price tag of 10/6 on it. It was the currency in England at the time. It's ten shillings and sixpence.
The subplot involving Ed Nygma and Isabella is remarkably similar to the main plot in Alfred Hitchcock's Vertigo (1958), but in reverse, regarding the two ladies' hair styles and color.