The two opera tunes that Londo and Vir are arguing about were both written by Christopher Franke, who also wrote the theme music to Babylon 5.
The "Markab doctor" that Dr. Franklin refers to is Dr. Lazarin, anticipating Confessions and Lamentations (1995).
The last episode to be written by someone other than series creator J. Michael Straczynski until Day of the Dead in season 5
Sheridan's cap displays the Earth Alliance Starship Agamemnon, his former command. Garibaldi's B5 shirt could very likely have come from the gift shop prior to Sheridan ordering it be yanked out, boxed up and sent back.
This takes place in August 2259.