In iOS, you must go into Settings>"Brightness and Wallpaper" and then toggle using the brightness slider.
P.S. You can toggle this with Siri in iOS 7.
iOS 6 is free.
Yes, when iOS 6 comes out it will be free of charge, just like iOS 5 and iOS 4 were.
Some ios 6 devices can be jailbroken.
Yes you can.
Probably not. The only OS for iPhone currently in beta is iOS 6. There are is no iOS 5.1.2 currently in beta and iOS 6 should be out within a few weeks. Unless a security hole in the current iPhone OS is found before 6 is released, don't expect an update to iOS 5.
No. It is just to soon for the devs to get an untethered jailbreak for iOS 6. Plus iOS 6 isn't available to the public just yet.
Yes. All iPad minis should be running iOS 6 and can update to iOS 7 this fall.
At the moment iphone 6 runs ios 8.1.3
Yes. iOS 6 will continues to support voice memos just like iOS 4, 5, and 7.
right now they do not have software for ios 6
settings/brightness
You cannot. If you buy a new iPod or iPad or iPhone, it comes in iOS 4.3.3 and you have a choice to update to IOS 5 or not.