Air pumps, at least that I've seen, never give any specifications at all. They just give an aquarium size which frankly is completely pointless as the number of gallons means nothing to an air pump. The depth of the tank maters the most. So for example, you need a stronger pump for a 20g tall than you do a 20g long tank.
As for the difference between wands, bars, stones, etc ... there is none other than looks.
You can power multiple things by using either a T connector, or by using gang valves.
Here is an example: Air Pump Accessories: AccuAir Aquarium Gang Valve by JW Pet