The Natural Philosopher wrote:

6/. Because of that you need rather more coil in the tank heat
exchanger for hot water.

7/. Because of that you need a supplementary imersion heater to get
teh water up to say 55 or 60C to make it sterile and safe in hot wate
circuits,.

If the water from the heat pump is cooler than the water temperature in your
cylinder, aren't you going to end up heating the house from the immersion
heater?