[mahout]

Take it from an old customizer and racer: if $600 is your budget spend it on wheels and tires at DiscountTireDirect. They'll even mount and balance them and ship for free.
We installed 205/45x17 Hankook's on 17x7x44 offset rims and they look good and handle well with occasionally tiny rub. Different antisway bars and lowering springs don't do nearly as much nor look as good.
After you do the tires and wheels then go with shocks, then lowering springs. Play with antisway bars last. Brakes anytime. Hawk makes a good street /track pad that we reshape to fit easily. We can supply for about $50 over the Hawk price.
If you are worried about heavy loads in the rear upsetting the suspension balance Monroe Max Air 791's are a pretty direct fit for $80 per pair at Advance Auto.. Check the 791 tho' cause I'm old and my memory's not as good as it was and I'm not in my office. Should be for a 93 Cavalier if memory serves. At about 25 psi preload it handles our test trackreal well. (if you want to see how we like to cruise VIR go to "Hyundai Sundae at VIR" on you tube). No, its not in a Fit but in an Azera. Before the end of February, we'll test the Fit in full trim. Handling always starts with wheels and tires. Good luck and cheers.