Just use the strength app and it will automatically count reps. At the end of a set it then goes to rest time. You don't have to double tap. Just start a set and it auto counts.
It occasionally misses a set but not an issue. I don't think any watch will give accurate calories for weights.
I haven't used my VA3 for weightlifting in a while so maybe something changed but you used to have to double tap to end the set. Without user action how is the watch supposed to know that a set is over?
Raising your BMR = elevated HR and vice versa. I your heart rate increases during exercise it is doing so to deliver more fuel to muscles. Does not matter if you are lifting weights, running, walking, skiing, swimming, plyometrics, etc. Any exercise that increases your HR is also increasing your caloric burn. So, if I am understanding your post correctly (I may not be) it is not right. Tracking your HR during exercise is the easiest way to determine caloric burn. Chest strap is more accurate then wrist based sensors because it is actually picking up the cardiac electrical pulse vs. using light to sense pulse in the skin on the back of your wrist.