Before you start bolting things to your car I would suggest you have the car in a good sound starting point - I dont know what mileage your car as done and you don't mention any service history but I would suggest (if this hasn't been done in the last 4 years 15K miles) getting your injectors cleaned, replace the fuel filter, replace the fuel pump - might as well uprate at the same time - new oil filter, decent oil, check / replace air filter, replace the brake fluid, check your brake pads and all pistons are free in the calipers, check the condition of the brake hoses - if original replace with braided items replace the spark plugs.
dependant on what you buy this lot could set you back 3-400 quid but you have a good known starting point for modifications and you have more confidence in the car starting and stopping when it is supposed to