Cost estimation for major renovation

We have been looking for a house for a long time and have now found one in our area (unfortunately an extremely expensive million-city), which would however need a complete renovation. This makes calculating the costs somewhat difficult, especially since we are not professionals and can contribute little labor ourselves (employment and 3 still quite small children...). The costs for renovations etc. have risen extremely in recent years, so we do not want to rely on older experience reports. We are currently trying to estimate the costs in order to get a rough overview of the expected total costs to make a purchase decision. The key data are:

- Semi-detached house from 1951, rectangular brick building, 200 sqm, double-shell masonry
- Full basement, ground floor, 1st floor, attic with hipped roof
- Plot 600 sqm
- Gas heating from 2006

Approximately everything would need to be renovated:

- New heating with heat pump and [Photovoltaik aufs Dach]
- Blow-in insulation
- Renewal of the electrical system
- Renewal of the water pipes
- Insulating and decking the roof (estimated 120 sqm roof area) plus installation of 3 large dormers
- Installation of approx. 16 new windows
- Installation of approx. 11 interior doors
- 2 new front doors
- 2 wall breakthroughs of non-load-bearing walls inside
- 2 new bathrooms (10 sqm and 5 sqm, mid-range, no luxury but also not cheap)

A new kitchen and new floors would also need to be installed.
I am fully aware that for some things (kitchen, floors, bathrooms, for example), the standard desired plays a big role and there are larger price ranges, so these are the items for which we do not urgently need an estimate. Maybe someone can still help and contribute some recent experience values for the other individual trades?
We are especially uncertain about the "big" items (heating, roof, windows, electrical system, bathrooms). It really only concerns a rough estimate, to which we would then add a large buffer.
Many thanks in advance!

- Semi-detached house from 1951, rectangular brick building, 200 sqm, double-shell masonry - Full basement, ground floor, 1st floor, attic with hipped roof - Plot 600 sqm

Non-load-bearing interior walls can however be bracing (and who even determined this classification?), typical for the year of construction are still lead pipes for water and cast iron for sewage, which only raises a question mark behind the sanitary modernization on a small scale. 200 sqm would be very generous for a semi-detached house from this era, presumably this means the total floor area including basement and attic? A double-shell masonry from this period will indeed require blown-in insulation and was executed more for material savings than for insulation considerations. I also very much assume a shared dividing wall between the semi-detached units. What about the other half - what condition is it in, and what are the owner/buyer planning to do with it?

We want to completely renovate a house from 1958. So pretty much everything out and make it nice or new again. Our architect estimated about 300,000-330,000 euros for the complete renovation. But the house only has 136sqm of living space.

We were once given a very rough estimate of 450k for a complete renovation of a house built in 1928 with a similar living area to yours (also around 200 sqm). This was from an energy consultant who went through the inspection with us. The target was KFW85 standard (I think, I don't remember exactly), and practically everything had to be done. Roof, insulation, windows, electrical system, sanitary/plumbing, floors, heating and underfloor heating, possibly facade insulation (with excavation).

Thank you for your answers! The living area is 200 sqm excluding the basement. The attic counts as well, those are proper living rooms, so (minus the slight roof slopes) also with normal ceiling height. The neighboring house is a very large multi-family house that is not identical and stands in a block perimeter development. It is estimated to have been built a few years earlier, and the "semi-detached house" was then attached to the end of this multi-family house. The multi-family house is fully rented. We had roughly also estimated renovation costs of €350,000-400,000. That would mean the house altogether (purchase price plus incidental purchase costs plus renovation costs) would just still be within our budget. By the way, the windows are made of plastic and only 10 years old. I suspect they could also be left in. However, they are insanely ugly and somehow disturb the overall appearance of the otherwise actually nice brick building. Well. We would have to think about that then.

To be on the safe side, I would estimate between 2300-2500 euros per square meter. It will be quite tight for you.