I cannot believe the amount of bad advice I'm reading in this thread.
-DO NOT get a fuel rail
-DO NOT get an IM
-DO NOT get a 70mm TB
-DO NOT get an ignition upgrade
Only highly boosted engines need to upgrade their fuel rail and their ignition system.
Only advanced NA setups need a larger IM and TB. The stock GSR IM flow well enough to support over 200whp.
You are still very early in the modifications game, and people are recommending things you won't need until much further down the road, if you will ever need them at all.
If your staying NA, you will NEVER need an aftermarket fuel rail or an ignition upgrade, and you won't ever need a 70mm TB either unless you get very big cams, build to high compression, and want a very high powerband with a raised redline. That's a REALLY big TB, and bigger isn't better in this area.
Your not going to want an aftermarket IM and TB until after you have cams AND high compression pistons. It will make you slower if you get them before then.
But I'm glad to see your making a good choice in getting a header and high flow cat next. That's exactly what I would do next, complete the I/H/C/E system. If your Tsudo N1 exhaust has a bottlneck at the beginning of it, you'll want to cut it off when you have you new Cat installed. I'm assuming by your choice of going with a 4-1 style header, your going for a high powerband. Therefore, I recommend that...
-If your going to do cams in the future, get a header with a 2.5 inch collector.
-If not, get a header with a 2.25 inch collector.