When to have brakes checked/replaced?

Hi! I have a 2006 Chevy Cobalt. It has about 55K miles on it.. we only put about 10 to 12K on it a year. And we live in Indiana.. in a relatively flat area.. not many hills or anything. How often should we have the brakes checked? And how often should the pads/rotors need to be replaced?

My husband and I are going to Tennessee next month, so I was just wanting to check. I'm not noticing any problems with the brakes that I now of.. it seems to stop fine...

But that brings me to another question. We have 4 almost brand new tires on the car.. we've had them balanced and rotated and everything recently. But ever since our vacation last year, we have noticed the car doing this shaking thing when we slow down to stop. Is this related to the brakes? New tires and balance and rotate did not stop it. It really isn't a horrible shake or anything. We just can't tell what's causing it. The steering wheel kinda shakes when it happens. We keep up on oil changes and everything that needs to be done...so we are just confused by this.

Thanks so much for your help!