Own work in new construction - what makes sense and is feasible?

Due to the presumably discontinued KFW55 funding, we are currently considering where we can save costs on our two-family house / single-family house with a granny flat. At a later point in time, if nothing else is possible, the question will surely arise as to how much we would have to downsize. The budget for the house could probably be managed well; however, we actually want to stay below the financial limit of what we can bear in order to be flexible and to shape family life the way we want (parental leave, etc.). We have two children (4 and 2) and are both teachers, so we are often quite flexible in the afternoons, but the work then has to be done in the evenings. One is a 50% position and the other a 100% position. My considerations are as follows:

[*] Floors and painting work were planned as [EL] anyway (our architect roughly calculated €20,000 for materials and €10,000 as muscle mortgage here, I think it can be done cheaper, but on the other hand we would like wood flooring). [*] The outdoor facilities of the old house will hopefully partly remain if the demolition/construction allows it but will then have to be gradually changed in [EL]. Some things will need to be renewed quite soon. [*] In some places we need excavation or slope support. Can that be done ourselves as well? [*] A garage is already on the property, it stays for now and is exclusive of the budget, so it cannot be “cut”. [*] We will prepare the attic for expansion, the rest (stairs, actual expansion) we will do ourselves later.

Are there things one can do well oneself, where the savings are worth it and which are easy to implement? I’m thinking of things like plastering? Where can one still save money with creativity? For example, is an exposed concrete ceiling or staircase cheaper than another version? We find that quite cool. I find wooden window sills nice, you would pay half the price per m2 compared to marble or whatever the general contractor asks for there (€150 per m2). We never wanted to assemble an Ikea kitchen ourselves again, but of course there would be great scope there, plus we already have a 5-year-old kitchen here that we could take with us. Or are these ultimately just gimmicks that don’t bring much and unnecessarily cost time and energy?

The basic things garden, painting, floor you already have.

If you can't tile directly then probably nothing more. Sloping is a tricky thing. You can do it alone if the stones can be lifted by muscle power. Alternatively, you would need to be able to operate a vehicle.

Here is some reading material:

https://www.hausbau-forum.de/threads/welche-eigenleistungen-habt-ihr-gemacht.33690/

https://www.hausbau-forum.de/threads/dauer-aufwand-eigenleistungen.31861/

https://www.hausbau-forum.de/threads/eigenleistungen-baunebenkosten-bei-neubau.26480/

What are you doing during the demolition of the old house? Are you gutting it yourselves, or are you having everything done? Depending on that, you can also help with things that take a long time, like chiseling grooves and pulling cables with the electrician. If he allows it.

At some points we need a slope or hillside support. Can you do that yourself?

It depends on how high and how steep. Roughly speaking, from about one meter it's better to hire a professional, but for a 2m retaining wall, as far as I know, a structural engineer has to be involved anyway. The material is also important. We are planning a hip-high retaining wall made of shell limestone blocks. The largest size you can still move with muscle power is about 40x20x20cm (+- a few cm). Above that you need an excavator with a grab and someone who can operate it, because an 80x40x40 block weighs around 400-500 kilos and then it simply becomes dangerous.

Where can you still save money with creativity? For example, is a exposed concrete ceiling or staircase cheaper than another version? We find that quite cool.

Exposed concrete is much more expensive than plastered if it should not look unfinished.

At some places, we need slope reduction or hillside support. Can this also be done by oneself?

You have already answered this question yourself by asking it.