Hygiene: How do people in Sigil perform their errands on natures behalf? And how does this vary from ward to ward? Is there a class aspect involved? Do the poor use back alleys, street corners and holes in the ground, or are there communal toilets where they can sit and chat with eachother while they´re doing their business?
Are there facilities for the rich where they can get their behinds cleaned and dried by summoned water and air elementals? And what are the costs?
What about body sizes? Are there particular facilities for halflings, and others for giants?
Diseases: Wherever large groups of people are gathered there´s a risk of disease. Wherever different species live together in close quarters there is a risk of relatively harmless diseases migrating from one species to another and becoming lethal. Sigil is a huge, crowded city with a huge variety of different species living side by side in cramped conditions.
Granted you have priests that can heal diseases. But do they perform these tasks for free? Is that a part of the price they pay to be allowed to worship their god in the City of Doors? Or do people have to pay for this themselves? Are there any companies that provide some sort of health insurance? Or is membership in a faith community a de facto health insurance, and a major incentive to give generously to the church?
If there is an epidemic outbreak, does the city pay for healing as a way to contain it? What if only one species is affected, say gnomes? Does the disease have to affect a certain number of species for the city to take action and for the factions to open their purses to halt it? Or is this a problem that each faction is left to solve for their own members?
What if the outbreak starts in the Hive ward, which is not unlikely? Will there be any attempts to aid the inhabitants, or will access to and from the ward be blocked until the disease has died out?