Welcome Racso!
You might want to visit the 240sx/Silvia/200sx section of this site to get a little more info. There is a wealth of valuable resources there that can answer just about anything you need to know. The search feature is a big help. Type in key words and fire away!!
You asked specifically about intakes and exhaust. The two most popular choices for the s14 intake are Injen and AEM. There is obviously several other options.... but these seem to be among the best, and fairly cheap. Exhaust choices are also numerous, but the Apexi N1, or N1 dual, and the HKS hiper are the most popular choices for cat-back systems. There is a lot of opinion in every direction on intakes and exhausts. Use the search feature to find opinions and make the decisions that fit your particular needs.
Stickers???!!! That's your call man, if you want to litter your car with crap like that... far be it from me to stop you! If you get product stickers, you should probably have the parts to back it up.... lest you might get the 'ricer' label.

When tastefully done, stickers are alright, but hey.... that's just my opinion.