The sound my car was making when it was the big end was fairly unique. At idle it was almost no sound, if you pooped the bonnet and stood there and reved it, as it was revving up, there is no sound, as it reaches it's peak is where it's at its loudest, so if you rev it up to 2500, and hold it there, I will be it's loudest here, when you let the throttle off again, the rattle will be a little quieter, or you may not even hear it. If this is what you are hearing then I would say 99% chance it's the big end. If it's not this then I don't know.
1. Exhaust, go for a 3 inch, anything else is a waste of time cos you'll have to upgrade it later anyway. You won't buy one off the shelf, go to a good exhaust shop and have one custom built, it can be done, it is a very tight sqeeze, but I have a 3 inch exhaust all the way through, so don't let anyone tell you it wont fit!
- Pod. A pod will fit straihgt onto the standard AFM, just get a good adapter plate.
-Extractors are for non-turbo cars.
2. EBC. I don't have much expirience with this stuff, but I do have a Jaycar one on my car and it is brilliant, $150 and it is programmable across 64 points accross the injector duty cycle, very programmable, works brilliantly. Just a little hard to build/set up. Oh, and yeah you can set it up so that it switches between 2 completely different maps, so you can have your missile switch.
3. Yes, the GT2871R does go straight on, but you need a GTiR exhaust manifold and you need to modify your exhaust slightly and a few other litle things. This is my write up from when I installed mine.
http://www.antrx.com/smf/index.php/topic,10342.msg197507.html#msg1975074. Why buy an aftermarket ECU when the standard one does everything you need it to? Get it chipped so that it can be modified, and have it tuned on a dyno.
5. Standard U13 injectors are 370cc, which I think works out to about 150kW at the wheels at the most. To change your injectors though you need to chip your ecu so it can be modded to suit the new injectors, and you should upgrade the AFM at the same time. A Z32 AFM is what I have and it allows you to tune a lot further.
Hope I've been helpful