Questions upon questions....?

So far, we only have an offer from provider A, provider B will follow, but I will not involve anyone else as this would only cause more uncertainty. It is also important that it will be a regional provider...

If providers A and B are rubbish, you shouldn't choose between the lesser stench. But well, with larger prefab house providers, there are certainly reviews from other builders.

There are correspondingly fewer reports for the smaller ones....

But there are certainly references. Ask your preferred provider.