What is an ideal plot size?

For the wishes of the TE, I would not go below 7-800m². We have afforded 1,300m², but we are in the village for that...

You lucky ones, with us it is twice as expensive again...

That's why there are also building areas with towel-sized plots, where a basement pays off. Or semi-detached houses are built - we had those before as well. But even on a 230sqm plot (house + garden) you can live well

Regarding the wishes of the TE, I recommend 800 - 1,000 sqm. That is more than enough to accommodate everything and also to be able to maintain it properly. I recommend planning for a ride-on mower.

We want a play area for the children with a climbing tower and a trampoline, space for a rotary clothesline, possibly a small pool, a spot where a gazebo can be set up, a fenced area for our indoor-only cats, and a bit of lawn, so that everything is not so cramped. If the house now has about a footprint of 200 sqm (including garage).

then about 26.5 m long and wide

Yes, and then it depends on where the access is from. But that was already said?! From the south, one might want to increase the garden setback in front towards the street.

I would take graph paper and draw: building volume 10 x 12 (or larger as desired), your desired garages, the 3-meter distances... then separate areas. If it is financially feasible, around 800 to 900, but your wishes are also doable with 700. Drawing is fun - and that way you can already get familiar with the property.

With us, the square meter costs 43.20 where I now think we will build. But we also live in the middle of nowhere.

A distinction is made between the humid Pampa in the east, which receives regular rainfall throughout the year, and the dry Pampa in the west