The bumper has to come off for both the Injen's and the Stillens. Removing the bumper is actually easier than it seems, I can remove it in about 15 minutes. Just be patient and careful and follow the DIY's and you'll be fine. As for the Fast Intentions, you can only buy that direct from Fast Intentions, you'd have to contact Tony.
This is his thread and he can be found
Here
Its a hot commodity and you'll pay a bit extra for it but in most of our opinions, it well worth it. Any questions about it too, i'm sure Tony would be more than happy to answer. He's got tons of knowledge and makes a top quality product. All the other parts i would definitely get them from FBNissan though. He's a great dude too.
And yes, save the tune for last, there's no sense in tuning when you will be retuning after other mods. I think you'll be quite pleased with your results no matter what route you take in the end.