Stock exhaust with Renthal Ultra Low handebars are a pretty good combination (I think) that makes the buzziness pretty low. That's what I have on mine and it feels pretty smooth. Yeah it'll have buzz because it's an i4, but it's not bad. I commute to class and back all the time which is 30 minutes away, and I'm perfectly comfortable. The 919 is a great motorcycle, PLENTY of power to keep you happy, really easy to handle at low speeds, and with my wider bars, it's pretty decent in the corners at higher speeds. For the brakes, they are good like most Honda brakes are. But don't expect to feel super strong braking power without getting steel braided brake lines. If you're over 25, insurance shouldn't be a problem. I'm 21 though, and insurance for full coverage is about $64 a month.
If you do want to buy a 919, I could possibly part with mine. I'm thinking on getting a sportbike. I'm in Williamsburg, VA with a 2007 919, excellent condition. PM me if you're not too far.