How should I fix up my car?

I want to put a body kit on my car, and buy new rims. I have a Mazda 3 hatchback. I know nothing about cars so I don't know exactly what to look for. If I buy new rims, do I have to get new tires? I want to shop online for rims and a body kit, but I can't find a good website. Any opinions or helpful hints?