the first mods are always the free ones... remove the spark arrestor from the pipe, you gain 5-10%, then remove the air box and gain another 5-10% last do the cam mod and you will gain another 30-40% (mostly bottom to midrange, it will have stronger pull). from then on you will have to spend money, then you have to decide whether you want to look good or go fast.
gnc 118, what have you been smokin' . 5-10% power increase is 2-4hp. 30-40% power increase means 12-16hp. it's unlikely you can get those kinds of increases with the mods you are talking about. but i guess you can dream.