i was wondering the same thing myself so i did a little research [albeit these figures are from a modern society, not a fantasy medieval society; in my opinion the d&d setting works best when you try to apply what we know about the actual world we live in and transfer that to a fantasy setting rather than trying to make assumptions about a medieval society [that most of us have a rather poor understanding of] and trying to transpose that into a fantasy setting]]. new york city, a city with a population of about 8,000,000 and about the level of crime [in my estimation] of the "average" fantasy city [that is to say, there are murders and other violent crimes though most of the citizenry doesn't live in fear, rough neighborhoods, elite wealthy neighborhoods with low crime, and a visible police force that seems to have crime pretty much in check] has a police force of about 39,500. so, for my campaign city of 100,000, i scaled this down to a city watch of 500, keeping roughly the same ratio. for your city of 14,000 you could go with about 70 members of the town guard in addition to those private guards and what [comparable to building security, diplomatic bodyguards, etc in ny?].