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
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.
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, it’s about how far they should be importing from. Many could probably do 80% of vegetables within ~20miles if the land around cities was used for horticulture rather than horses.