Swann's Way (vol I p 134 ff). Swann in Love: Notes May 2010

p 134 |Portrait of Mahomet II by Bellini (also used in describing Bloch): 

And Swann felt a very cordial sympathy with that Mahomet II whose portrait by Bellini he admired, who, on finding that he had fallen madly in love with one of his wives, stabbed her, in order, as his Venetian biographer artlessly relates, to recover his spiritual freedom. Then he would be ashamed of thinking thus only of himself, and his own sufferings would seem to deserve no pity now that he himself was disposing so cheaply of Odette's very life.

La maison dorée restaurant around 1860. Wikipedia has a history and this page shows the evolution of the building on the corner. (p. 526/384)

• Les Filles de marbre (1853), a play by Théodore Barrière (1823–77)
• Beuzeville-Bréauté 

Possible letter-writers:

1. Basin, Duc de GUERMANTES, as Prince des Laumes: (brother of Charlus & husband of Oriane). Consistently unfaithful: 481. Swann suspects he wrote the anonymous letter: 506-10.
2. Palamède, Baron de CHARLUS (nicknamed Mémé; brother of Basin). At Combray, rumored lover of Mme Swann; 45, 137. Go-between with Odette: 442, 449, 456. Swann suspects he wrote the anonymous letter: 506-7.
3. M. d'ORSAN (Swann’s friend..."they held the same views about everything", though was said to have indelicate relations with a certain wealthy woman).  Swann suspects he wrote the anonymous letter: 506-8.

A procuress is a female pimp. Interestingly enough, this subject was popular among Dutch artists, including Swann's Vermeer! Here is a discussion of his painting The Procuress (1656); click on the title to see the whole image.  Two other paintings on the same subject are here and here.