The first hovercraft was invented by Sir Christopher Cockerell in 1956. It started out with a few kitchen items and a blower. A cat food tin inside a coffee can with a blower on a flat surface turned into a hovercraft. It was first used on water.
airplanes are the same thing as hovercrafts... but only hovercrafts have a louder engine
on a cushion of air
yes
hovercrafts
Why are you asking where to find hovercrafts? But I would have to say, that scientists are trying to build some, or aliens are, but you should have known that already.
yes.
4 ft
6 inches
They both fly I think 
walk
Very good conditions!
"Hovercrafts" are available now and have been.