The Samsung Brightside is more a feature phone rather than a smartphone. Snapchat can be installed on devices that run on iOS and Android operating systems.
Snapchat is an app available for smart phones. It is currently available for IOS and the Android softwares. Snapchat uses your data plan to send and receive messages, therefore, it will not cost you extra in your bill for sending pictures through snapchat.
No, some of them do not require ios os. For example, this app: apps4trip.com/instagram-app.html works perfectly with android
iOS 8 is customizable by users with programming skills check out - codenameone.com/blog/ios-8-installs-customizing-the-pull-to-refresh
Restoring a backup merely restores the apps, data, and contacts you had saved on the device. It won't downgrade it from iOS 8 to iOS 7.1.1.
ios 8 can be installed on ipad by first registering or have your device UDID registered by a developer and then download the iOS 8 beta and install it on your ipad
Jail breaking a IOS 8 phone is hard to do. You will have to reset the phone all the way.
iOS 8 should not affect your phone at all. It should be safe.
No
As of May 2014, Apple has not said when the iOS 8 will be released. Speculation is that it will be released around the middle of September.
To save movies on Snapchat you can download the SaveSnap app on itunes.apple.com/us/app/savesnap-save-snapchat-pictures/id756298885?mt=8
Sadly you cannot legally downgrade an Apple device. It would require dangerous hacks to do so.