The iPhone 4 can only support from iOS 4.0 to iOS 7.1.2. There is no way to get any higher iOS Firmware due to the older hardware that is built into the iPhone 4.
No
If it's bricked it has to be restored by Apple to factory settings.
Yes, you can run iOS 7 on the iPhone 4.
it depends on which country you are located at , in US it shall sell for around $150.
Extra info: I have Terminal, A few emulators Installous and a few ringtones. If I upgrade, what will happen to these things?
You ll get for not jailbroken . Factory unlock will sell for more.
You can get free ringtones for a non jailbroken iPhone 4, 16gb online at mobyware.net.
Yes you can, but expect some iOS functionalities that are on, say the iPhone 5S won't carry over to the iPhone 4.
The iPhone 4 can currently run up to the latest version: iOS 7.1.
iOS 5 will be compatible with iPhone 3GS as well as iPhone 4.
Yes, if you update it to iOS 5.1.1, there is an untethered jailbreak out.
Yes, it just needs to be running iOS 4 or later.
Since ios 7 is designed for the iphone 5, it will probably make the iphone 4 slower.