Settlement house 1954 - complete renovation possible?

Hello everyone,

my wife, daughter and I have found a small old house in our place of residence and work (small town in BaWue, 8,000 inhabitants) with the following features. Further below there are still open questions.

[*]Year of construction 1954, 110 sqm living space with 380 sqm plot (densely planted with half a dozen fruit trees)
[*]Pictures see below.
[*]Location about 800m from the town center: 30 km/h zone; hardly any traffic, as only a few houses follow and then the next hill begins. Daycare 5 minutes on foot and Edeka 7 minutes. Train station 10 minutes. Work by bike 15 minutes. (The employer is also the driver of real estate prices here)
[*]Heating (oil with wood log supplement), roof ridge and facade renewed around '99
[*]Double-glazed windows, but only partially with plastic
[*]Fully basemented (220 cm ceiling height)
[*]Garage parking space in the basement (easily enough for our bike fleet)
[*]Sale without realtor for 160,000 euros

Sounds maybe good at first, only the house is quite worn out in terms of the interior and also needs to be cleared out. We were already inside with an architect and fortunately found no moisture or building damage. Our plan is nevertheless a complete renovation. An inspection by a KfW-accepted energy-efficient house engineer is still pending. There is no energy certificate yet. Probably incredibly bad due to the thin brick walls.

Interior finishing, electrical system and water pipes to be replaced, underfloor heating installed, kitchen, bathroom we estimate will cost about 85,500 euros:

Construction debris & bulky waste	Own work		1000
Kitchen screed			1000
Laying tiles			2000
Structural engineer			1500
Wall removal/re-plastering/painting	Own work		8000
Bathroom screed			1000
Bathroom tile laying			8000
Shower			3000
Toilets			2000
Washbasins			1500
2 glass doors to the garden			6000
Electrical work	Own work		5000
Pipe replacement	partly own work		10000
Flooring material	Own work		5500
Front door			3000
Kitchen	partly own work		20000

Then there is the energy-efficient renovation on top. Comes to 135,650 euros:

Underfloor heating			7000
Brine heat pump + technology			24000
Hot water tank			2000
Overlay insulation + roof covering (140 sqm)			35000
Exterior wall insulation and plaster (200 sqm)			30450
Windows (26 in total)			18200
Photovoltaic panels			8000
Inverter			2000
Ventilation system			9000

Total costs for the house are then about 385,000 euros. So very, very steep and aimed at low consumption. The numbers are mostly rough estimates. It is not yet clear to me whether the planned measures will be sufficient for KfW 55. KfW 430 would then add another 30,000 euros, besides the child construction allowance.

My questions:

[*]Feasibility: The basement slab will remain uninsulated. -> Does that break the KfW 55 energy saving concept?
[*]Have we overlooked a major cost risk? Loan requirement would be 230,000 euros, which we would probably get at 0.9% interest for 20 years. Monthly payment 1,000 euros. Besides the payment for the loan, we still have 2,300 euros per month left for saving/repaying after deducting all costs. I am (still) sole earner.
[*]Is 12 months (provision interest) enough time? I am somewhat skilled in craftsmanship, but unfortunately not blessed with the necessary time.
[*]Is there anyone with a similar project in finished condition? We would be grateful for any tip.

Building plans and pictures:

Ground floor
Attic Here the kitchen has meanwhile been replaced by a bathroom.	Basement But we do not want to use the bathroom there.

You are really going all out with the renovation! Is there a reason for the expensive heating system and roof insulation? On the other hand, I would definitely insulate the basement; it would be negligent not to do so (unless you insulate the basement walls from the outside).

Currently, the plan is to extend the insulation down along the side of the house wall. There is a staircase inside the house leading down to the basement. One could insulate the basement ceiling, but then the basement itself would be freezing cold and the stairwell would probably become a thermal bridge – at least that's my guess. What would be the better approach?

Brine heat pump due to the higher efficiency. But the house is small – presumably it does not need to be drilled deep and I am overestimating the costs.

The roof is tight, but the tiles already look old. I would want to replace them as a precaution. For the insulation of the sloping ceilings in the attic, is there any other option?

A very charming, rustic little witch's cottage. But economically, this would be a project for a quirky high earner to pimp this property into an "energy-efficient house." In this respect, despite all the charm, I see this more as a plot of land than a modernization project. Overall, there would be three (with a pinch of salt) fairly comparable properties in the forum. The exterior wall with 25 cm (probably solid brick) is absolutely contemporary and therefore not unusual. As is common locally, would the practically 420 euros (plus demolition costs) per square meter of land apply?

The house is worth modernizing. The total costs will certainly be able to compete with new construction costs... 400,000 is ridiculous

Have we overlooked a significant cost risk? Loan expenses would be 230,000 euros, which we would probably get at 0.9% interest over 20 years. The installment would be 1,000 euros. Besides the loan payment, after deducting all costs, we still have 2,300 euros per month left to save/pay down. I am (still) the sole earner.

Sounds great! Don’t overextend yourselves with the personal contributions. Financially, there is more room if necessary. What about the electrical work?

P.S. I love these settlement houses with their charm

The standard land value of the city is €175/sqm (as of 2017). However, there will be no new development areas in the foreseeable future. We are a few years too late for that. These houses now all stand on plots of 400 to 600 sqm. Total prices supposedly from €600k to €1200k.
At least that's the rumor mill in the village

The price is of course steep, I also suspect because the house is theoretically ready for occupancy. From a purely economic point of view, the whole thing is nonsense. But can a new building with those standards be cheaper?