Well if you are not tuned start there. An I/C is something you should really watch, the stock one isn't horrible compared to the FoST but should be upgraded at some point. If you are not tuned then there is no point though. The best thing to do is ask yourself what your goals are. I would run Meth with a Hybrid or BT upgrade you will get better results unless Meth is something that doesn't bother you when it comes to cost and maintenance.
Start with E30 tune, then I/C then go from there. In terms of power and I/C doesn't add power but will make consistent power. Like mentioned above my FoST would have a 100 degree rise on one 3rd gear pull, the FiST I have seen 30. Cooler air equals more mass which equals more fuel and results in more power.