Ordered Edge 130 but looks like that VA4 does not support extended display or it does?
You don't have to start an activity on the VA4, but you can (I've never seen the point). Just set the VA4 to broadcast heart rate and the 130 should be able to pick it up. It will be as accurate as it can be, as it's specifically set to read & broadcast heart rate ... so it's kind of like an activity that doesn't record.
When you set the VA4 to broadcast hear rate, you'll get a notification the battery life will be reduced.