Help Me Out!!!

hey, im getting ready to buy my friends 2001 celica GT soon as i get rid of my truck and i need some ideas for performance mods. my friend got the car from a guy that used it for a show car so it already has body kit, wheels, suspention, exhaust and some other small stuff. ivbe talked to a few people and found only a few mods can be done such as the headers, small shot of nitrous, or jus go all out and get a turbo (which i plan to do when i get the money saved up to have it done) is there anything else that i can do? ive also noticed that there are more performance parts for the gts. i kno the engine puts out more HP and all of that but what is the actual difference in the engines? sorry to be asking such stupid questions and all but ive been drivin nissans since i was 16 and havent ever had to learn about 2 dif engines for the same car :( there is one pic of the car on my site if any1 is interested in seeing it, will be more to come jus gotta figure out why my friends pics arent coming to me when he emails them!!!

http://maxima.cardomain.com/id/gimpy835