Definitely go first, mod later.
Yeah, yeah, driver skill is where 90% of your improvement potential is, but if you like to play with your car...
Get a little experience, learn the classing rules, and figure out what class you want to be in. Mod accordingly, based on what you perceive (after getting some seat time) to be the major weak points in the car. Then, most of the time, it's tires, suspension, then a toss-up between brakes and horsepower.
Or, skip the mods and go to driving school.
But none of this is really necessary if you just want to have a good time.