IOS8 stands for internet Operating System. The number 8 recognizes the current number of the operating system, meaning that there were previously 7 other operating systems made before the 8th was released.
NO, it is not.
Yes, the iPhone 5 will be able to get the IOS8 update.
Only if you have an iPhone 5S or newer.
You will have to download the IOS 8 on the iPhone 5c. This is easy to install.
No, it cannot. The earliest iteration iPhone that can carry iOS 8 is the iPhone 4S.
No, it won't be able to support the demands of iOS8. The oldest phone that is listed as being able to support that iOS is the iPhone 4S. However, it's generally not recommended to do so, as it was designed for the bigger iPhone 6 and iPhone 6 Plus.