^ This is good advice. Collect all the supporting mods over a period of time and get it all done at once, or do as much as you can yourself. For decent gains you'll want to do injectors and intercooler at the same time. Also if you are planning thinks like CAI or headers do that at the same time too.
I'm not fussed by sticker, looks alright but would be better if it wasnt bubbled/ripped. I reckon replace it with the large P-WRX sticker.