Freshwater station and buffer tank: technically better choice?

We have now decided on a brine heat pump. Two heating installers have offered different technical variants: 1. Alpha Innotec heat pump, 400l domestic hot water storage, and no buffer tank 2. Alpha Innotec heat pump, fresh water station, and large 800l buffer tank What is to be preferred now, or how can I find out the advantages and disadvantages?

800l buffer tank only for the fresh water? How many people do you want to supply?

What flow rate do you need?

Are the 800l for the heating circuit?

The 800l are for, as I understood, for the heating and when fresh water is needed, this warm water is used for hot water preparation via a heat exchanger/fresh water station. In other words, the water in the tank is not domestic water.

800l buffer only for the fresh water? How many people do you want to supply? What discharge rate do you need?

So we are about 6-7 people in the two apartments. The buffer is actually only for heating.

If 800l heating buffer then clearly offer 1!