One of the partners at my work races in LeMons and Chumpcar, he started in Autocross...
When I asked him for advice on how to start, he told me this:
-Make sure all your fluids are at the right levels, maybe even change them.
-Get everything out of the car that doesn't need to be there (not so much seats, but random things, stuff that can fly around.
-Get a Snell 2010 helmet, 2005 ones are cheaper but you'll need to buy another one soon if you decide you want to go to the track.
-Don't bother with any mods yet, learn your limits and your car's current limits, then see what you can do to improve handling.