We have a well and a cistern here.
My parents had the well drilled. In the well hangs a deep well pump that has been pumping water into a pressure tank since then. The only thing that had to be replaced after almost 30 years was the pressure tank because it had rusted through. Of course, I also renewed several other things at the same time.
The cistern was only added a few years ago because the annual costs for rainwater disposal were too high for me.
Got a 4 m³ plastic tank. Connected the rainwater pipes. All done by myself. And after about 6 years, it was already turning a profit.
But now to what would like to know.
Whether a cistern is sufficient for you or not cannot really be said.
How large the cistern can or should be depends on the connected area (roof, driveway, etc.) as well as on the amount of rainfall and of course also on the size of the garden and on the plants that are there. And of course also on the budget.
I can only say how it was here in the last 2 summers. Since we mainly have a kitchen garden here, quite a bit had to be watered. Because you want to harvest something, after all. So there was actually a sprinkler running somewhere on the property almost daily. Therefore, I assume that at least 3 m³ were needed daily. This means that our cistern, even if it had been full, would only have lasted a maximum of 2 days.
It wouldn’t have worked here without a well.
So if possible, have a well drilled for you (not driven) with a pipe diameter of at least 125 mm. Then hang a powerful pump inside, put a pressure tank in the basement, and connect it to the pipe going outside.