What is the appropriate loan amount?

No, that's not enough.... at least if you're building in a dead end. I'm speaking from experience here. Basically, it depends on the regulatory office on what they allow. And how accommodating the crane operator is. Ours demanded 6m, but in the end, 3.50m was enough. But most likely, you will have to have a stabilized crane pad made on the construction site.

So it's not a dead end. If we have to build this reinforced crane platform, what does it cost and what does it mean?? Do you have any information on that?

The site manager is provided by the supplier - hopefully not a beginner
The builders arrive with huge articulated lorries, so I am already concerned about the road width! Thanks for now.

The tractor-trailers are not your problem... the crane is...
Keyword escape routes.

They can check that in advance. Let your seller come and he should give you a written statement about it. These are binding with the provider.