My 7 mile route has a big hill and a couple of red lights/stop signs. I average 14-18mph depending on wind conditions. This is on a loaded down, fully upright bike (~45 pounds).
As far as top speed, I tend to max out at 30mph coming down the big hill on the way home, and that's with me pedaling hard and crouching down low. My bike just isn't made for speed. Definitely don't ride faster than you feel comfortable.
My regular speed on flats with no wind is 18-20mph.