Well for garden irrigation - improve idea - please provide input

With the sq 3-40 you only have a maximum delivery head of 55m. This means that at the top of the hose only about 2 bar will come out, assuming the 30m borehole. In the tank you also need a proper pump again to bridge the 20m height difference. So from the maximum value on the nameplate, two bars are lost again there. Therefore, I would prefer to buy a real proper pump with which you can reach everywhere on your property.

Does that mean in liters or m³?
100,000 l or 100 m³?

I can't say, as it depends on how much of the garden we plan to design and what we do where - I think about 1500-2000 sqm will be cultivated, the majority will remain wild and forest.

I am now a bit further along, combining with the [Regenzisterne] is apparently not the best idea, so a strong pump and direct connection. With some delay, the pressure concept makes sense to me. Now I will have the well builder come, let's see how deep it really needs to be (so far that was his estimate) and where the whole thing fits best.

Is it still even sensible to build a well? Groundwater levels are dropping, and let's say in 10 years you may no longer be allowed to water your garden. There is a small town nearby where there is already a ban on lawn sprinklers and pool filling, a restriction on watering utility and ornamental gardens, and cisterns may not be refilled. This indirectly puts your well out of operation.

Water scarcity is a local problem. Withdrawal and direct use return a large part of the water directly.

Is it still even sensible to build a well? Groundwater levels are dropping and let's say in 10 years you won't be allowed to water your garden anymore.

As writes - there is locally no groundwater problem here and therefore no hesitation with the approval. No, "sensible" probably isn't the case if you look at it monetarily, you are right. And if at some point the authorities close my well, my life won't get worse. Therefore, I don't consider that a relevant risk. Take it as a combination of a man's toy and a more carefree feeling when we increasingly cultivate land and don't use drinking water for it. Viewed this way, the money is not badly spent.