Is purchasing a house and complete renovation affordable?

No advertising brochures, personal experiences within the family circle. I don’t see the problem either. The radiators don’t care which machine heats the water to 50°. Of course, the heat pump is no longer as cheap to operate as in a new building. But neither are oil or gas heaters, especially not in the long term.

The boomers choke on that because in their time they still financed with double-digit interest rates. I have the impression that the term “Darwin Award” (video tip for that: Mai Lab) means a lot more to me than the term boomer does to you. :D

There the wish is the father of the thought. Heat pump without surface heating? Good luck. Don’t read so many advertising brochures ;)

80sqm apartment heated with heat pump, previously oil. Only new windows and the ceiling above insulated – so manageable energy measures. No ETICS, built mid-60s. 33-radiator. Location Lower Rhine, designed for -12 degrees. Flow temperature +/- 35 degrees at -10 degrees last winter.
Heating costs over 50% below the previous heating costs with oil heating – calculated on the respective comparable electricity/oil prices.

No advertising brochures, real life.

P.S. Can you even call it surface heating with so much surface area as those thick things provide?

The whole thing should not escalate into a "which heating is better where" discussion.
The fact is we have the opportunity to buy the house at a lower purchase price.
The fact is also that we want to have children.
I have to plan a little and can't just live in the here and now.
Sure, if having children doesn't work out for whatever reason, the house and garden are oversized.
But renting a 3-room apartment now and then realizing at the second child that we want to buy a house after all because the apartment lacks space—I don't think that's the right way.
We look every day on various real estate platforms for houses.
But cheaper than grandma’s house it just doesn’t get.

The whole thing is not meant to turn into a "which heating system is better where" discussion.
The fact is we have the opportunity to buy the house for a lower purchase price.
The fact is also that we want children.
I have to plan a bit and can't just live in the here and now.
Of course, if it doesn't work out with children for whatever reason, the house and the garden are oversized.
But renting a 3-room apartment now, only to realize at the second child that we want to buy a house because the apartment lacks space, I don't think that's the right way.
We look for houses every day on various real estate platforms.
But it just doesn't get cheaper than grandma's house.

The problem was already outlined a few pages earlier. Your framework conditions regarding income, loan requirement, and resulting payment don't fit together. Or did the colleague summarize that incorrectly?
I still have about 4k net in mind, and 500k financing needs? Then you can’t manage a payment even with 2% amortization. Paying down less means you don’t reduce the outstanding debt.

There are also about 25,000 euros in additional costs for the notary and property transfer tax. Per child, you can expect one year of reduced income. This may mean that your monthly loan installment costs more than 50% of the household income. You could say the house is perhaps cheap for the region, but still not cheap enough for you.

... it was 5400 net and currently there is a savings rate of 2700 euros and already self-saved 200000 euros.

350000 euros purchase price, 250000 euros renovation needs (I would work that out with a priority list), 50000 reserve, notary, but NO property transfer tax and NO broker, since it’s grandma’s house, so no expenses in that area
==> 650000 euros ==> 450000 euros loan.

In the construction financing calculator I played a bit with the equity because it automatically also calculates the property transfer tax.

The rate would therefore be 2257 euros plus additional house costs.

There would still be 30000 from the parents in reserve. Could raise the renovation pot to 280000.

Who managed to save 200000 euros by 28, the rate should also be possible. You just have to plan the children and parental leave carefully, but until then maybe there will also be salary increases.

I don’t see it generally so negatively.