yeah made another thread about this and it was closed. what you want to know has been covered many many times. try a bit of searching and you will soon get answers.
to answer your questions, well one in particular, "what sort of gains can you expect", that depends on so many variables. depends on the turbo, the amount of boost you run and various other things. you would be best of starting by working out what sort of power you want to make, what sort of characteristics you want (low end power or a lag monster) and then basing your mods around that. do that before you go asking questions about what turbo you should use, etc. another good question to ask yourself is how much you are willing to spend. a new turbo, injectors and ecu (won't be able to put in larger injectors without it, and can't safely put a bigger turbo on without both) will set you back around the $4500 mark (give or take a few hundred dollars), depending on turbo, etc.
so work all that out, then do some searching in the forced induction section of the forum. you will find everything you need in there without needing to start a thread