There was a report done on a city reasonably close to me: https://www.bristol.gov.uk/files/documents/1104-who-feeds-bristol-report/file it was quite influential ~10yrs ago

No, not with today's tech and without using energy to replace sunlight. Once we have an abundant source of renewable power then yes, maybe. But the question would then become "why?". Cities are dense for reasons that cause residential buildings to be more profitable than vertical farms. Unless you remove those reasons I think cities will prefer to import food from the countryside

Yes, but the city in question can not be a mega-city or conurbation that is really big(think New York metropolitan area or São Paulo metropolitan area), population would need to be more evenly distributed. Also you need to have an ring of agriculture around the cities, so it is important to build good infrastructure all-around so people can be comfortable in other places besides these very big cities.

One of the basic laws of ecosystems is: the biomass of a herbivore must be 10 x smaller than the biomass of the plant they eat, and likewise 10 x between predator and prey.

In a city, the biomass of humans is huge. Unless the city is a literal space ship powered by its own fusion reactors and utilizing direct chemical synthesis to create feedstock for edible yeasts and bacteria (skipping nearly all plants and skipping absolutely all animals)... without that, we can pretty much forget about a city feeding itself, or it will be an extremely large and flat city which some would call "countryside" (or an energy-intensive city with multi-storey artificially lit greenhouses).

The space ship scenario - skipping all animals, skipping most plants and getting the goods from the simplest possible food chain - of course assumes a rather uninteresting menu driven by necessity. People wouldn't be satisfied with such a menu, if they have the possibility of eating more diversely.