There's several kinds of gunsmiths. You should figure out which "type" of smith you're thinking of.
First, there's the guys who take down guns, inspect, clean, lube, change parts as necessary, gage wear points, etc and put the weapon back in service. Let's call these folks 'repair smiths.' I'm not being demeaning; there's a real lack of these types of smiths who can get into a gun, inspect/clean/oil and get back out quickly. For a gun with nothing wrong with it and only needing a clean/inspect/lube, you should try to get it turned around in 40 minutes or less.
For those who have an ability to memorize the internals of a LOT of guns, there could be real money in this skill in the retail smithing situation at a flat $50 to clean/inspect/lube a gun. Some of 'em you'll be in & out in 20 minutes, some will take an hour. When you average it out, you could be making $60 to $70+/hour, plus margin on parts.
This level of smithy doesn't need a lot of expensive equipment, but he needs a bunch of books of parts and manufacture-specific knowledge, a bunch of hand tools (some specific to the gun at hand), and a parts inventory.
Second, there's the guy who does higher-level repairs - re-barrelling, chambering/fitting/making new parts, re-blueing, bedding, re-crowning muzzles, etc. You'd need a lathe, possibly a mill, grinder(s), etc.
Third level of gunsmith are the guys who make guns. When I say "make guns" I mean that they can start with a block of wood for the stock, a barrel and possibly an action and/or lockwork. They make the rest of the gun. Quite frequently, gunmakers don't do repairs, they only make custom guns.