Thanks so much, Gary.

Coil outlet superheat varies with type of system. Generally speaking, a freezer should have 6-8F/3.5-4.5K superheat, a cooler should have 8-10F/4.5-5.5K superheat, and an A/C should have 12-16F/6.5-9K superheat.
What figures for evap outlet superheat & condenser sub-cooling should be used for an air-to-water heat-pump?

At what operating temperature would the refrigerant mass charge determination be most appropriate - startup Tc,sat 35'C; or hot end Tc,sat 70'C?

I have no given mass charge to work off in this case & have to determine it in-house.