Power, I can't comment on. That seems like a pro thing, and for them, it is power:weight ratio.

I think heart rate is more important for regular guys like us, and pretty easy to get a Bluetooth heart rate monitor chest strap and pair it with your GPS.

For cadence, you want to not be mashing the pedals, but spinning them by pedaling in a circular motion. Not so fast that you're winded from spinning so fast, but fast enough that you're using the gearing to make progress, not just brute force.