People often under-estimate the potential gains from reworking the suspension and spend all their money on their enigne. a little bit here and there on the suspension will make a big difference. It's no good having lots of power if your suspension can't put it down to the ground.
as for the sockets, here's what i'd go with:
1/4" Shallow + deep - 4-13mm
3/8" Shallow + deep - 8-19mm (+ Spark plug 5/8", 13/16" & 18mm)
1/2" Shallow + Deep - 10-32mm
Standard 1/4", 3/8" & 1/2" ratchets
Flex head 3/8" ratchet
1/2" breaker bar
You usually won't need all the deep 1/2", but if you can get a set with all of them in, it's worth it. As for impacts, i rarely use 3/8" impact and don't own a set or a 3/8" gun. I only have 1/2" impacts and have yet to be caught short.
10-27mm Impacts, Shallow + deep, plus Hub nut sockets (30, 32, 33, 34, 35, 36mm - All Deep)
For an impact gun, an Ingersoll-Rand 2135 is the best you can buy, never heard a bad word about them. strong, reliable, powerful, light etc.. and in the long run, cheap as they never cost you anything other than purchase price and some gun oil.
That's What i'd go with. pretty much the same as the base of what i've got, and rarely do i need anything else. But you will want to consider hex/torx bits, torx sockets etc. i don't know of any Japanese cars that use triple-square bits, but some do use double-hex. (although, that's mostly for Toyota headbolts)
Hope that's of some help,
Moose.
