Newly built single-family house - gas or air heat pump + photovoltaics + storage?

I think gas is not a disaster. Unlike existing buildings, with an [Energieeinsparverordnung] house you have a relatively low heat demand. Therefore, gas consumption is also limited.

I find it important to build the underfloor heating in such a way that switching to a heat pump is possible without problems. Low supply temperature of max. 30 degrees, preferably equally long heating circuits, room-by-room heat load calculation, … I would take care of that sooner rather than later, and overall you will have to study the topic more if you don’t want something 0815.

An air-to-water heat pump, an aroTherm Plus from Vaillant, was offered.

Unfortunately extremely expensive. We can get it too, but only because of very high subsidies last year.
Without subsidies, I would go to providers with a significantly better price-performance ratio!

We asked ourselves the same question for our house construction in 2022 and initially decided on gas

What a pity.

since the heating can later also be (easily?) converted to hydrogen.

What’s the point? Instead of fourfold efficiency with the heat pump, a fourfold loss with hydrogen production?
Expensive and bad for the environment...

With the current issues in DE, the EU and around the world, I cannot comprehend how anyone could come up with the idea of installing a gas heating system in the year 2022 and beyond.

We asked ourselves the same question for our house construction in 2022 and initially decided on gas, since the heating system can later also be (easily?) converted to hydrogen.

I can hardly imagine that, because hydrogen requires completely different and significantly higher-quality materials. Neither existing pipes nor pipe connections are suitable for hydrogen, and probably not the heating system itself either.

Oh come on, the "green" hydrogen will fix it. I fully trust the luminaries Altmaier, Bareiß & Co.

We have underfloor heating upstairs and downstairs

Good. Is there a heating load calculation? How is the underfloor heating designed? Max. flow temperature? Have the desired temperatures for the individual rooms been set? Unless a 40-degree flow temperature is required, I would also tend toward an air pump.