The 2.4 inlet mod has been very hit and miss. With the increase in flow through the inlet, to make use of it would really need better flow around the head meaning porting. TBH, even before my car was supercharged, it already had head work and cams and the 2.4 inlet made no difference at all when fitted. If I were you I would be looking at getting a sport cat put in, get a 2.5 inch custom downpipe and a 2.5 inch catback system like a Magnex. Milltek would be my ultimate choice but they are only special order and you have to have a minimum order of 10 systems bought through Courtenay Sport on the Vectra system. So, based on that, Magnex is the next best option.
I used to have a standard 2 inch system with a Remus center section and it was very noisey and not a lot of go. I then got the Milltek and the performance gains were great. The torque was the most noticeable with an increase of 18lbs torque. There's a lot to be said for a good tuned exhaust system from a tried and tested manufactuer. They spend LOTS of money developing exhausts that produce good gains.
I went through 3 different setups before I settled for what I've got now.
Oh, as for mapping, whatever you do, leave this until you have finished all your mods to get the best out.
;-)