I found some useful resources for building fantasy cities when I was looking for RPG DMing resources, those might be useful. Although those are typically based on the European middle ages. I don't have any at hand right now, but I can check later. There are even fully built cities one can copy (though I don't think how many of them are free to use.)

I think sewage systems were developed relatively early, with private toilets even. In general a lot depends on how wealthy the city is, and if the wealth is spread out equally, and how big it is, especially when it comes to the question if freestanding houses make sense. As for water supply, that's probably an area where you could do a lot with some household magic, that'd depend on the magic system.