Interpretation of the soil survey report

The general contractor will offer the service if needed, but has already stated that he cannot make the most competitive offer and that we should gladly approach a separate earthworks contractor.

Ouch ouch ouch - unfortunately, I now read more than just a faint hint that you came to the general contractor contrary to my most important mantra without a tender :-(

First concrete offer is available:
(1) Excavation of 60cm, including frost apron + drainage
- Excavation and disposal of soil: €2,600
- Backfilling with F1 soil and compaction: €2,300
- Drainage around the house including soakaway chamber: €4,400
- Excavation of frost apron or strip foundations: €600
Total: approx. €10,000

(2) Excavation of 150cm, without frost apron + drainage
- Excavation and disposal of soil: €6,500
- Backfilling with F1 soil and compaction: €6,300
Total: approx. €12,800

My questions:
(1) From your perspective, is there a qualitative difference between the two options or should the decision be made solely based on price?
(2) How deep are strip foundations typically, and are they always continuous all around? In other words, does option 2 actually save the frost apron or are strip foundations always equivalent to a frost apron?
(3) Can the soakaway chamber of the drainage around the house also be directly used as an overflow protection for the planned cistern in the garden?

First concrete offer is available:

... between which lie so many worlds that either the bidders have read the tender sloppily or at least one of the two wants to take you for a ride or you have skimped on a competent tender issuer. My dead grandma without glasses can see that this doesn’t fit. An offer bot quoted snippets from your request and wrote prices behind them. The gambler’s strategy is to bet that the offer will please you because - A: they are the bidder with the lower unit price in the positions, or - B: they are the bidder with the lower total price, or - C: they are the bidder with at least one individual position that a competitor has not even listed. Do you want an expensive learning experience or to build a house? If the latter, then you should take the tender more seriously.

... between which lie so many worlds that
either the bidders have read the tender sloppily or at least one of them wants to pull a fast one on you
or you have skimped on a competent tender issuer.
My dead grandma can see without glasses that this doesn’t fit.
A bidding bot has quoted snippets from your request and written prices behind them. The gambler’s strategy is to bet that you will like the offer because
- A: they are the bidder with the lower unit price for the items, or
- B: they are the bidder with the lower total price, or
- C: they are the bidder with at least one individual item that a competitor didn’t even list.
Do you want to make an expensive learning experience or build a house?
If the latter, then you should take the tendering more seriously.

You are aware that these are two different alternative positions from one provider?
Besides, I have roughly summarized the positions from the offer here for better readability.
So I don’t quite understand how you come to your respective conclusions...

(3) Can the leach shaft of the drainage around the house also be used directly as an overflow protection for the planned cistern in the garden?

Absolutely not. Overflows belong to the rainwater sewer, for both the cistern and the drainage. Otherwise, you risk that during continuous rain the water stands in your leach shaft and backs up into the drainage. But that is exactly the case when you need the drainage.

(1) From your point of view, is there a qualitative difference between the two options or should one decide solely based on price? (2) How deep are strip foundations typically and are they always all around? In other words, does Option 2 actually "save" you from the frost protection strip or are strip foundations always equivalent to frost protection strips?

As a layperson, I wonder where the position is to pour the frost protection strip here. In Option 2, you can directly do the floor slab; in Option 1, there are only trenches for the frost protection strip. So something else goes on top. By the way, a frost protection strip has no structural function, unlike the strip foundation. What you need and how deep it goes will be told to you by your architect or structural engineer.

Definitely not. Overflows belong to the rainwater drain, both for the cistern and the drainage. Otherwise, you risk water standing in your soakaway pit during continuous rain and backing up into the drainage. But that is exactly the situation where you need the drainage.

We don't have a rainwater drain; we have to infiltrate on the property.

As a layman, I wonder where the position is to pour the frost skirt. In option 2 you can pour the floor slab directly, in option 1 there are only trenches for the frost skirt. So something else is added on top.
By the way, a frost skirt has no structural function, unlike the strip foundation. What you need and how deep it goes will be told to you by your architect or structural engineer.

Yes, you're right. I've noticed that too. However, so far I have assumed that a strip foundation (if deep enough) automatically also counts as a frost skirt. But here, like you, I am just a layman.