Prospective Audi Buyer

Hey All - I'm a newbie here, but it seems to be a great site with great input! Hoping you can shed some light on some questions...

I'm considering purchasing a '03-04 A4 1.8T and have read a bunch of your posts regarding replacing the ECU with and APR chip. I've driven the stock 1.8T and, coming from a V6 in my current car, it seems somewhat unresponsive by comparision. So my questions are:
1) how much of a difference does the chip actually make? Does it feel like you're driving a hopped up 4 cylinder, or does it feel more like a 6 cylinder?

2) Does anyone know about how the chip affects the lifespan of the engine? Should I be concerned with shortened life due to a higher-performing chip?

3) I've read a little about APR's chip and its ability to allow me to toggle between chipped and non-chipped modes... but even if using this feature, how likely would it be for the dealer to be alerted to the mod? Don't want to void a warranty, if at all possible.

4) Last question - most of what I see on the posts is regarding 1.8Ts. What about the 3.0? I'm assuming that chips aren't an option for the 3.0? If one were to choose between a chipped 1.8T (APR stage one) and a 3.0, what would you guys choose and why?

Thanks for the info...and sorry if some of this stuff is pretty basic. Just wanted to get the facts before I decide to pull the trigger!