Hey Ace,
Production Houston did a good job summing it up, but here are my 2 cents:
1. Latency is as low as 4 to 5 frames to iOS devices and decoders. Here is a recent test using the Teradek Clip:
2. Audio is embedded into the stream over SDI, HDMI, or via the analog audio input. It does not increase latency. IFB is also possible, though it is only one way and requires use of our free Sputnik server.
3. Latency will not increase with more iPad connections, but there are limitations. For example, a Cube can take up to 3 iOS connections at one time as long as the main stream is disabled. If you connect any more, then latency will increase. If you have a high quality main stream going, then only 2 iPads or so can connect to the Cube.
If you have any further questions, just shoot me an email: Mike @ Teradek [dot] com