What would be the approximate cost for a partial renovation?

Hello :)
I hope I am in the right forum here.
We are currently in the process of buying a terraced house (built in 1958). The current owner told us that the heating system and the windows would need to be renewed. Since the electrical system was renewed about 30 years ago, we would also like to renew it, as well as the pipes. In addition, the stair steps (2x 12 steps each) would need to be closed.
We would also like a new washbasin and a new toilet.
To enable financing, we are supposed to list the costs that will still arise for us to the lending institution. For this, we should base it on average values and rather estimate a little higher...
A few more details.
The house has 90 sqm of living space, divided into three bedrooms, a living room with a [Wintergarten], a kitchen, and a bathroom. 5 windows are to be replaced. We would choose lockable plastic windows with shutters (not electric).
In addition, there is a large floor-to-ceiling window with a balcony door installed in the large bedroom. The old windows should be disposed of.
The current heating is an oil heating system. A gas pipeline is being laid in the street this year. The house is already registered for a gas connection. We would also choose a gas heating system. With additional renewable energy, this can be subsidized.
The radiators might also need to be replaced.
Our theoretically planned budget would be €15,000 for the windows, €20,000 for the heating, €5,000 each for electrics and new pipes, €2,500 for the stairs, and €2,000 for the sanitary installations.
It is really only about rough price estimates that could be realistic.
If more information is needed, I am happy to provide it.

Thank you :)

We are currently in the process of buying a terraced house (built in 1958). [...] In addition, the stair steps (2x 12 steps each) would have to be closed.

Are the stairs that steep or are the rooms that low?

Since the electrical system was renewed about 30 years ago, we would also like to renew it, as well as the pipes.

That sounds like wrong ideas regarding the indie-jet-time-catapultability of old buildings. You won't get the house any younger than the state of the electrical system renewed just thirty years ago. As for the sewage pipes, there is probably still cast iron. Ask the neighbors. Several houses must have been fundamentally modernized already, and the original plans are not unknown to all. There will be a lot of valuable information about how the houses are constructed.

P.S.:

I hope I am in the right forum here.

Yes, here you will find and with slightly older but also quite small terraced houses according to today’s taste; and , where you can take a detailed look at the construction sites a house from this period has to offer in .

It is actually only about rough price expectations that could be realistic.

So for me it is: - Heating (including installation of underfloor heating): 45K€ - Electrical: 17K€ - Doors & windows: 47K€

Overall, however, difficult to compare. I have a complete renovation of a listed townhouse, after renovation approx. 128m2. 100% of the technical systems will be new. From my feeling, your electrical costs are rather set low. For the windows, I have no feeling. For me, these are wooden sash windows according to the requirements of the monument authority, which will be significantly more expensive than simple plastic windows.

Window is the only thing that you do not have to at least double in my opinion.

The installation of a new heating system does not come to 20k. Even with many radiators, probably not. I would first take an inventory of the electricity. The standard from 1990 usually fits. With your budget, you can at most expand the electricity. Completely new, you’d rather come to about 15k. I can’t say anything about windows. Things like sinks can easily be done yourself.