Heat pump, what are the experiences with tank size?

Hello,
we are currently building a single-family house with 180m² of living space in Bavaria.
Now we are having an air-to-water heat pump installed and also a water-bearing stove to additionally generate hot water.

Our construction company said an 800l tank is completely sufficient and this is now planned.

However, another stove builder says that this is far too little, that we will have problems if it is cold for a few days and will not get properly hot water.
He also said that a water-bearing stove only causes unnecessary costs instead of bringing any benefit?

Does anyone have experience regarding the size of the tank or the water-bearing stove??

hm., we were told that (we are 3 people) at least 300 L up to about 500 L would be sufficient. Usually, you don't bathe immediately one after the other. However, after bathing (about 200 L), there should still be at least 100 L left for showering. The water will already get about 60° C warm, which should be sufficient according to the specifications (bacterial protection etc). (for showering anyway)