- Heating can be new, but doesn't have to be. Assume a low-temperature boiler based on the year of construction, which doesn’t need to be replaced. Those things run indefinitely, a chimney sweep friend calls it the Mercedes of heaters. Normally, you don’t have to replace heating pipes. Since it’s a closed circuit with stagnant water, nothing happens there. Radiators are a matter of taste; the old ribbed radiators work at least as well as new ones. If you switch to gas and replace all radiators, 8-12k.
- Bathroom / guest WC I would always do as well, it’s a feel-good thing. If you have everything done here, start from 10k upwards, no upper limit.
- Windows / interior doors / front door: can be done, but doesn’t have to be. Are the windows and doors defective? Or just a matter of taste? These are all jobs that can be done fairly quickly and with manageable dirt, so can be done at any time.
- Floors / walls: definitely do, at least because of the electrical work. Floors you can do yourself well, estimate 3-5k material costs. Walls can also be done yourself, no idea 2-3k?
- Electrical: what does the current installation look like? 3-core with FI and enough outlets? Then expand and lay LAN as well. This is also a job you can do yourself well. Material costs are manageable. If there is still classic neutral wiring and no FIs, everything new costs about 10-15k professionally, including LAN.
- Opening to the kitchen: depends on the statics, whether something has to be added to the ceiling. If not, you can do it yourself, costs nothing except sweat and tools, of course.
- Insulation of the basement ceiling: simple and quick to do, with good material a few thousand.
In my opinion, you can get by with significantly less if you renovate sensibly.
P.S. Water pipes could be replaced if you open the walls anyway. If they are already copper, maybe not necessary, but with iron pipes it would be a good idea, RNK is mostly chalky.