With regards the cotter pins loosening up? Oh, just put a wrench (10mm, I think) on the nut and see if it has loosened. Don't over-tighten it, because the nut isn't meant to tighten it, only to keep it from coming out. After a ride or two it should stop loosening if it is loosening at all. But you don't want to ride with it loose. That will deform the pin and it will never sit right again, which means you'll need to file it flat very carefully(!) and very little or get another. You be able to tell if it has a problem because the crank arm will move on the spindle as the pedal goes over the top. If the bike shop installed it right you shouldn't have a problem, but it is good to check it when it is new.

Enjoy the bike!