Yes, any USB flash drive will work as a memory card on the Xbox 360.
They are different versions of Xbox 360s. The arcade has games that come with it while i think the pro has more memory.
All Xbox 360s can play all the Original Xbox Games on this list http://www.xbox.com/en-US/games/backwardcompatibilitygameslist.htm provided that you have an Xbox 360 Hard Drive and can update the game with Xbox Live or through a computer and USB flash drives or DVD/CDs
All of the Xbox 360s may play games. They are priced differently because of either memory space or package deals.
Buy 2 xbox 360s and put a cable between them.
All 360s can connect as long as you have the correct items to connect to xboxlive
All the Xbox 360s are compatible with Kinect. You just need to be sure you have enough memory free on your XBox for associated updates for Kinect users.
No, all saved data is kept on the hard drive, or memory card.
X360 Slim.
All Xbox 360s.
£200 / $300
Yes
I am Cristian, his cousin, i have been to his house, he has 3 xbox 360s. One in his bedroom, one in the couch room and one in the study