just pick up tools as you go. assuming you have all the standard auto related tools, i would get:
angle grinder, will change your life.
Mig welder, which will make you want a Tig welder...
drop saw.
a good vice.
weld stuff and learn about different materials. nobody welds stuff good for ages, if somebody tells you otherwise they're talking shit. my first welds were terrible lol.
when you start learning about welding, whole new oppertunities will open up for you in terms of making your own parts, braces, cages, everything. all i can say is go your research into what type of welder you want (basically only Mig or Tig) and how you should sue it and what to use it for.
speak to some members who are know to be big fab specialists, being an NS member i'd refer to str8e180 and other influential members for advice. it will help you in the long run and i know a lot of people in the trade will be more than willing to give advice.
good luck with it =]