front mount intercooler lowers the temperature of aire going into the engine. as cold air contains more oxygen it makes a bigger explosion in the cylinder therefore more power. a lot of people rate a side mount intercooler made by turborevs. its a direct swap for the existing one
induction kit. doesnt do much really as itll just suck in hot air from the engine (heatsoak) so is a bit pointless unless you were to get a dedicated feed one like a pipercross viper, bmc, k&n apollo or one that moves the filter to behind the bumper. carbonio, k&n typhoon. personally id go fo a pipercross panel filter in the air box and smooth the airbox. use google to find out about that theres loads there
decat. the cat is more of a particle filter on a derv so itll be a bit more smokey. but itll make the turbo spool up quicker and at slight lower revs. the back pressure wont matter on a turbo as it wants to get rid of exhaust gas asap