Never designed a heat pump system but have worked with a few. This was around the mid 80s and I hope their efficiency has improved. When the OAT (Outside Air Temperature) dropped below 32 F or 0 C you had to manually turn on what they called emergency heat. The system was blowing cold air with OAT below 32 F. Useless as teats on a bull. Turning on emergency heat just added some electric elements to make heat.
Take measurements to determine your system efficiency. Rather than mess around with CT Clamps if this will be permanent I would just use regular current transformers like this.
Add a burden resistance and offset the AC voltage developed across the burden resistance then feed that into your Arduino or like uC. Your code can decide how to handle the loads. No clue as to
So you want to average the four readings?
All in all you can look at the blower air out to determine when to kick in electric elements or the OAT. You mention a 63 amp load so for the electric heating element(s) I would just go with a good quality SSR and that's all you should need. The SSR is in a permissive loop where the main current draw is not to exceed whatever you have available and make sure you consider changing loads. Projects like this work much better when the supply is more than adequate for all loads.
I would sit down with a piece of blank white paper and a pencil with a large eraser and start listing what you want to happen and when. Step by step. Manual On/Off bypass is simple enough to incorporate. Web based user interface (GUI) should not be a problem.
Ron