Can't help you with the first one...but I'll take a shot at the other 2.
On the Cessna 172, the fuel vent is located on the left wing. With the addition to the fuel cap vents, there's a total of 2 vents on the left side and only 1 vent on the right side. As a result, it is easier to get fuel from the left tank. It'll take it out of there until about 10 gallons are burned off then start drawing from the right side. When you shut the plane down, the checklist says to place the fuel selector on either the right or left tank. This prevents fuel from flowing to each tank. This is in case the plane is parked on a bank, and all the fuel would flow into one tank.

For the Pipers, the name Cherokee applies to the basic PA-28 model. There are several derivitaves based on configuration, etc... For example, the Warrior is a 160 hp Cherokee. The Archer is 180 hp. And the Cherokee Arrow is 200 hp and complex. But they all fall under the PA-28 designation.
Hope this helps.

-MJ