I'd stop asking about this stuff piecemeal and commit to saving up for a complete package upgrade. Based on what you seem to want, I'd call up a place like ATP and find out what packages they can put together for you, including software.
Stay FAR away from ATP software! The only way to go BT without giving up an arm and a leg and the entire contents of your wallet is to do it yourself but it requires research, time, blood, sweat, and tears. Please note i said "RESEARCH" which doesn't mean posting questions everywhere in attempts to get people to spoonfeed you information, as many people do. Head over to the 1.8T forum on VWVortex, and just start reading. I'm an automotive technician by trade, but when it comes to performance stuff the bulk of what I've learned about the 1.8T and how to make it roar came from sifting through tons of information online, always being careful to determine what info was accurate and what wasn't. You'd be amazed what you can learn to do by starting small and gradually working your way up.
Anyway, after that rant its only fair I tell you that bigger injectors are pointless until you are installing a bigger turbo, and whatever size/boost/hp is intended of that setup is what determines what size injectors you need.