Build new or buy an old house?

Now I say 2.

Windows from at least 1998 are OK. Have them adjusted once and then it's fine. New ones do not pay off financially.
The heating is also good for many more years. Pay attention to maintenance.
It says that the attic was insulated. Also good!
Facade insulation can be done. It is subsidized as far as I know. The problem here is the small roof overhang, which causes additional costs.
The location seems quite good. Judging by the appearance, regular investments have been made.

Only you can judge the price. With the 410k from 1., it will definitely not stay like that.

Simply together with the appraiser. If there's nothing serious, I would probably prefer that.
The location has to suit you and the floor plan.

Where is property 1 supposed to be built if the plot share of 70,000 euros is already fixed? That must also be a plot of land, right? Or is that just a potential offer from Town & Country, where you actually don’t know anything exact yet, including the exact price of the plot? That would be more reasons for me to prefer property 2.

Are these then also sloped properties?

Usually, additional costs are incurred for founding on these, the garden layout is more complex, and one has to consider how to use the slope, possibly a cellar as in offer 2.

Is all of this already taken into account in offer 1?

No, with offer 1, it would have to be on a relatively flat plot of land without a slope.