Start off with a Brownell's Master screwdriver set, the one with replaceable blades. You will use this the most, buy the BEST.
Buy extra sizes of blades for the screwdriver set.
A good Allen wrench set.
A LARGE screwdriver for removing shotgun stocks.
Brownell's replaceable tip pin punch set.
Brownell's "starter" pins for the above punch set.
A roll-pin punch set.
A round-head pin punch set.
Brass and plastic drifts.
Assembly picks, and hooks. (Dentist's picks).
Several ceramic stones--triangle, square, round, etc.
An Optivisor or equivelent magnifer visor.
A good bench light.
A rubber or plastic bench pad.
A high quality small "all-way" swivel/tilt bench vise.
A set of hammers--brass/plastic, and steel.
A GOOD adjustable-tension hack saw with finer tooth blades.
A jeweler's "wire" saw, with blades. (I use size #3).
A LARGE selection of files. (You can't have too many sizes).
Swiss file set.
Handles for all files.
A file card and a large, chisel-shaped nail, to clean files with.
Silver BEARING (3%) SOFT solder and flux.
Silver HARD solder (braze), and flux.
A "Turbo" torch.
Several types of small pliers.
A flex shaft or Moto-tool, with as many types of polishing/cutting
tools as you can find.
A large supply of Cratex rubber-bonded abrasive wheels, bullets,
and cylinders, with mandrels.
A "hell box". This is so called because it's Hell to find anything in there. Everytime you visit a hardware store, look for odd size/shape springs, pins, washers, and screws, in short, anything that looks like it might be useful around guns.
A Brownell's catalog.
A Gun Parts catalog.
As many gun exploded view, and disassemble books as you can find. Especially the NRA's Gun Disassembly books.
Gun specific tools. (Colt cylinder bushing wrench, S&W rebound spring tool, etc).
Jerry Kunhausen's Gunsmithing books for specific guns.
Collect books, catalogs, and any other gun info you can get.
Of course, if you don't intend to do some jobs, such as the soldering, you aren't going to need those items. Get what you need first.
With the above tooling, you can do an amazing amount of work.
As you need it, you will add more.
The ESSIENTIAL items are the GOOD screwdriver set, the standard pin punches, the Optivisor, the bench light and pad, the vise, the stones, and the Swiss file set. Also the catalogs from Brownell's and Gun Parts.