it's good if you can't detect any ammonia.. it means your tank is cycled!
getting the bacteria from a well established tank (either by using the filter media or some gravel) can potentially speed up the cycling process a LOT. and the more bacteria you can get, the better the head start will be.
however, you have to be careful not to take ALL the bacteria from the established tank (you wouldn't take out all of the gravel and all of the filter media, for example) cuz then that tank would have no bacteria (or not nearly enough anyways) and it would have to start cycling all over again!