welcome to the LOC! :) I'm new to all the car tuning stuff too, but I'll try and chime in.
with the stock tranny you could easily get 350-400 I think. Smooth is the expert in this area - he's beentheredonethat. It really depends on the tuning. And as far as exhausts making your car sound whiney/ricey, I don't think you'll find that problem with the IS, the 6 cylinders sound a lot beefier than a civic's 4 - but it depends on your definition of "whiney" so I'd check out all the videos on youtube first.
I have the JoeZ intake pipe and a Blitz drop in filter than I clean out every now and then to keep the air moving smoothly, and I'd say this is definitely the most bang for the buck upgrade. The SRT is pretty sweet, but I think it's overhyped. The JoeZ is simple and works with the stock air system already in place. And if you're planning on going turbo in the near future, don't bother with anything intake-wise, the turbo will replace it.