It's possible (I'm not saying likely - but it happened to me so it's foremost in my mind) that the "non-smooth" rotation of the crank could be due to the bottom bracket being shot. Hopefully not, since it would cost more to replace than I'd be willing to spend on that bike. In any case, ride the heck out of it and get a better idea of what you want for your next bike, and save up for said next bike.