Q1-4: Simple answer is you would need either a CABLE or a 4iiii HRM to bridge the ANT+ signal to the tablet. At the moment you cannot connect directly to the tablet using ANT+ so it needs to be bridge to BLE. It does not matter if the tablet supports ANT+ or if you get a dongle on it you would still need either the CABLE or the 4iiii HRM to bridge the signal. The same goes for iOS devices just as an FYI.
Q5: The answer is yes.