Home construction company stops working - Continue alone, but how?

There was a contractually guaranteed completion date that has been overdue since June. We then set them in default and set a grace period, which has also expired.

How much time (and what further communication from whom to whom) was there between the expiry of the grace period and his wishes yesterday?

We have made claims for rent, interest, and co.

Were these claims agreed upon as penalties in the contract?

How much time (and what further communication from whom to whom) was there between the expiration of the grace period and his wishes yesterday?

Almost 3 weeks. No significant communication, except that the electrician was supposed to be on site last week. This was confirmed by the electrician and the construction company until mid-last week. Then an SMS from the electrician that he would not come and on the same day an announcement from the construction company about yesterday's conversation.

Were these demands agreed upon as penalties in the contract?

No, there is no regulation about compensation for damages in the contract at all.

Just to make sure. The property is yours and not purchased from the contractor? How is it then that 70% payment is due at a closed shell? And why does the neighboring house have the same contractor? This smells a bit like a developer and a payment plan according to the real estate agent and developer ordinance.

A contract without penalty clauses is bad, and the payment plan is not good for you either. If the contractor is in insolvency proceedings, you have a problem and where there is nothing, even a good lawyer cannot get anything out. Think now about to what extent you would be able to finish the house yourself with additional money or sell the shell to minimize damages. I assume there is no completion guarantee?

Think now about to what extent you would be able to finish building the house yourself with additional money

That's exactly what I wrote in the original post.

Then an SMS from the electrician that he is not coming

And what does he say about the reason?

Exactly that is what I wrote in the original post.

As I wrote earlier today, there is a lot to do and you certainly won’t manage that with craftsmen for the 74k. With the mentioned additional payment and some own contributions, it might work better. But it won’t be fun. I would advise looking for an architect who will tender and coordinate the outstanding trades as soon as the legal situation of the previous general contractor is clarified.