Screed on wooden floorboards over crawl space and more

Hey! We bought a single-family house from 1938, renovated in 1988, and want to move in at the end of the year. From 15.11. we will have the key and want to renovate a few things beforehand. So time will be tight, and we urgently need advice on how to plan the renovation with whom, without becoming poor.
A few facts about the house: 125m2 ground floor and upper floor, partially basement, under a 12m2 room there is a poorly accessible crawl space with a wooden construction as a ceiling, Buderus gas heating from 2006, 5kWP solar system – own use planned only in 5 years, solar thermal.
Plans and questions about the floors on the ground floor: Living room and bedroom have linoleum flooring on wooden floorboards, below are wooden beams and below that concrete in the living room and the crawl space (12m2) in the bedroom. In the hallway there are tiles that could be tolerated, but it would be nice to lay new vinyl with cork insulation (8mm thickness overall) in all three rooms. Here the problems start: what would be a sustainable solution for the subfloor in the three rooms (total 50m2)? Screed in the living room? Screed on wood in the bedroom?
Then the heating topic. Does it make sense to partly switch to underfloor heating and partly use the old radiators, to later gradually convert? Does it even make sense to get rid of the gas heating because of the photovoltaic system and because gas is getting more expensive?
Topic government subsidies. We were told that most KfW subsidies are not worthwhile because the required standards are very expensive.
We still have many other topics and would probably need comprehensive advice from people who understand the connections and dependencies. Who do you talk to for that?

I wouldn't necessarily put wet screed on an old wooden construction. Depending on the condition of the floor, possibly cover it with OSB or if everything is crooked and uneven, level it out with dry screed. Are there more details about the floor?

Unfortunately not. The seller of the house is accommodating but they still live there. If I can only plan the floor tearing in mid-November, moving in by the end of the year probably won't work... but it has to. Details in terms of thickness and condition of the floorboards?

We bought a single-family house from 1938, [...] A few facts about the house: 125m2 ground floor and upper floor, partially basemented, under a 12m2 room there is a poorly accessible crawl space with wooden construction as ceiling,

That is very unusual and even more than usual a reason for more knowledge from the building file.

and want to move in at the end of the year. [...] Owner-occupation planned only in 5 years,

I don’t understand that.

Details in terms of thickness and condition of the floorboards?

Examine the condition of the wood from below. Does the floor sway or creak? Is the floor uneven? Is the floor insulated? Is the floor boarded from underneath? If you have viewed the house, you surely took photos, right? Is there a brochure?

I don’t understand that.

Then don’t cut off the relevant parts of the text:

Buderus gas heating from 2006, 5kWP solar system – self-consumption only planned in 5 years, solar thermal.

The system will be a pure feed-in system since it was installed around 2006. In 2026, the feed-in tariff will expire, so it will be converted to self-consumption.

Questions about the floors on the ground floor: living room and bedroom have linoleum flooring on wooden planks, underneath are wooden beams and below that in the living room concrete and in the bedroom (12m2) the crawl space. In the hallway there are tiles which could be tolerated, but it would be nice to lay a new vinyl with cork insulation (8mm total thickness) in all three rooms. Here the problems begin: what would be a sustainable solution for the subfloor in the three rooms (total 50m2)? Screed in the living room? Screed on wood in the bedroom?
Then the heating topic. Does it make sense to partially switch to underfloor heating and partially use the old radiators to then convert step by step later? Does it even make sense to get rid of the gas heating because of the photovoltaic system and because gas is getting more expensive?
Topic state subsidy. We were told that most KfW subsidies are not worthwhile because the required standards are very expensive.
We still have many other topics and would probably need comprehensive advice from people who understand the cross-connections and dependencies. Whom should we contact for that?

You can contact a site manager, civil engineer, or architect who works with existing buildings for your project. Or a general contractor who does conversions.
But please be aware that _nothing_ will happen this year anymore. Even if you start doing everything yourself now, you will fail due to the lack of materials, processing time (screed, drying, etc.). This is completely unrealistic.