Apple Tv (3rd Gen) App Development What do i need?
The new TVSJ Framework or the TVML won't work on my 3rd Gen Apple TV?
Apple said the 3rd gen Apple TV will not run tvOS when means you can't develop any app on that device. If you do want to develop, you can buy a 4th gen.
Do I have to develop everything via iOS swift/Objective-C?
Nope, Apple TV runs tvOS which have its own SDK. But the frameworks are very similar. tvOS also got some of its own SDK which iOS don't have. You do need to develop in Swift or Objective-C.
Can I test/install my app without a paid developer membership ?
Yes, Xcode 7 allows you to test app on device without paid account. Though to install app on Apple TV, you will need an USB-C cable.