Do not buy a tap set.
Do not buy an Irwin or other hardware store brand tap or die.
They are all the cheapest, poorest quality taps in existence.
They are all plug taps - not made to start new tapped holes.
They are all carbon steel taps instead of HSS High Speed Steel -
High speed steel has been around since since 1937 - 80 years - there's no excuse to sell carbon steel taps
You won't use 90% of a tap set
Buy multiples of the ones you will use = say 3x
Buy a HSS, two flute spiral point tap
Sizes ?
NC is more common, say
#6 -32
#8-32
#10-24
1/4-20
3/8-16
1/2-13
If you're into folders then
0-80
1-72
2-56
4-40
Buy one or two good tap handles, like a Starrett 91 or 93 (various sizes)
or a Greenfield GTD
Watch this for sizes and styles
Buy the tap handles - wrenches used, get the taps new
These are inexpensive, but quality imports
These are CHEAPER than the hardware store crap, but 10 times better.
I can chuck these up in a drill press and power tap steel in a new hole without breaking.
http://www.sowatool.com/Product/14/266/700
Got a tap chart ? starrett has a nice PDF free
Get the number drills for each size and keep them sharp / separate for tapped holes
A metric hardware store set may be useful if you work on cars, to clean out a dirty or rusty hole. But that's it - and you can buy that set used if it's just for that.