Tips for establishing a new garden in a new development area

I am not looking for a solution that allows me to dig up the garden in 3 hours

I probably exaggerated a bit with the description

We tried it with a hoe (3 prongs in front) Yes, you can get into the ground after repeatedly tapping and then break out larger pieces

The larger pieces can then also be reduced, but as I said, it is very labor-intensive
I hope that with the electric tiller I can dig it up a little easier piece by piece

Perhaps a comparison: You can wonderfully drill holes in Ytong walls with a Parkside battery screwdriver. Maybe also in sand-lime brick. For the reinforced concrete ceiling, however, you really need the Hilti rotary hammer. Compressed clay with stones is the reinforced concrete among soils. That's our experience as balcony gardeners so far. In sandy soils or newly piled topsoils, you can probably use an electric tiller.

A friend of ours also has a Parkside drill and it worked wonderfully on [Kalksandstein] but also on a concrete basement wall or concrete ceiling.

When would be the optimal time to dig over the garden?
after it has rained and the soil is wet/moist?
then it should be easier to get in with the tiller for the first time digging over

I am not looking for a solution that allows me to till the garden in 3 hours

Don't underestimate that. Yesterday, I needed an hour per pass with the tiller. After 2 passes, the soil was still rather coarse in some places. For our natural garden that was fine with me, but for English lawn you need to go over it more often. A good time is probably when the soil is still slightly moist. If it is too wet, everything sticks to the tiller. If it is too dry, it becomes hard.

so you could recommend the Einhell cultivator? yes, it’s clear that it will be exhausting

That depends on your soil. If you have a lot of stones in it, you won’t have any fun with it. The stones get stuck in the tines and are then very difficult to remove.