my $.02 - in my opinion.. number one priority is to make the car safe. number 2 is to make it reliable. then can chase more performance. of course, sometimes these things overlap....which is good.
if engine staying stock... stay with stock intake, filters etc. these are well sized and cause no loss of power.
time and money better spent here making sure engine is in good state and set up correctly. do not assume anything. check everything right from the beginning. have seen engines with the top dead center displaced - which moves everything.
oil - sythetic multi grade. maybe 20W50.
replace all the hoses, belts, fluids. drain and flush block. spend money and time checking/cleaning/repairing radiator. if rules allow, replace water pump radiator fan with an electric one mounted to the radiator. this actually saves a measureable amount of power.
brakes - stock brakes are very powerful and more than adequate for a stock engine. rebuild the calipers. ir\f you have any questions about mastercylinders, replace them. replace brake hoses with braided stainless steel ones if possible.
put in a high temp brake fluid. bleed the system often. most important, put in good brake pads for track work. the worst possible place to save. spend the money properly and the car will stop like crazy - over and over. these cars are light, this engine is not powerful, no way you can overtax the stock brakes (with proper pads and fluids).
#1 - replace ball joints, tie rod ends, bushings. buy good quality. personally i recommend poly for all the bushings.
#2 - wheels and tires - Tires are biggest determinant to track performance. not sure what you face there, but in the US hard to find decent street/performance tires in
14". still a decent selection in 15"... but most require (work best) a minimum 7" wide wheel. buy biggest wheels rules will allow.
is difficult to fit 15x7" wheels in giuila rear wheel houses, but can be done if offset right. especially if you move the limit strap
mounts. wheels should be LIGHT. you do not have much power to work with, don't want to sacrifice what you have spinning up heavy wheels.
3. - get car lower. how low depends... are you driving it on the street as well? then can not go super low, makes life a little simpler. make suspension stiffer. Keep it
simple. shorter and stiffer springs. something in the region of 1200 pounds/inch in front and 200 in back. heavier sway bars. something like Koni shocks.
4. - get a performance front end alignment. if can, get the rear axle cambered (easy to do) - but of course can not be changed much. at least check. on my super, the
rear axle actually had some Positive camber - BAD. -.5 degrees is about all can get.
5. - set proper ride heights to give good chassis balance. if you can, get the car scaled. for what is worth, most of the "canned" spring packages give a decent start
point on ride heights. from there can adjust front ride heights to bring into good balance.