Construction financing as a young couple including own contribution

Good day,
we have been dreaming of owning a home for some time. Since construction prices have skyrocketed, I always wanted to simply buy a house and renovate it. However, unfortunately, these prices have also exploded in our rural area. In contrast, plots of land are still inexpensive.

General information about you:

[*]Who are you? M/F couple, unmarried
[*]How old are you? M29/F27
[*]Are there children? no
[*]Are children planned? Yes, probably one, maximum two
[*]What are your professions? Service technician / educator
[*]Are you employed, self-employed, retired, housewife, househusband, etc.? Employed
[*]How many hours do you work? 40/38

Income and asset situation:

[*]What income do you have (gross/net)? together approx. €4500 net, whereby I have a company car. (So no costs for mobility, normally €4900 net)
[*]How much child benefit do you receive?
[*]Other transfer payments like parental allowance, sick pay, etc.?
[*]How much equity do you have? €110,000
[*]How much equity do you want to invest in the house project? €60,000

Expenditure situation:
Expenses that are already included in other positions can of course be omitted. This list is not final and can be expanded or summarized as needed. Please make sure to specify all costs monthly, even if they occur only annually!

Housing costs:

[*]current cold rent
[*]current warm rent including everything €900
[*]electricity
[*]gas
[*]water, sewage, garbage fees, street cleaning
[*]telephone, internet, mobile phone

Mobility costs:

[*]monthly ticket for bus and train (also for the children!)
[*]car loan (or savings rate for a new car)
[*]insurance
[*]taxes company car, for second car about €200/month total
[*]fuel
[*]repairs
[*]other
[*]Is there a second car, motorcycle, scooter? Please specify all points again!

Insurance costs:

[*]private health insurance (also supplementary health insurance, daily sickness benefits, etc.)
[*]liability insurance (also animals)
[*]capital or term life insurance
[*]pension insurance (also Riester, Rürup, etc...)
[*]disability insurance
[*]accident insurance
[*]household insurance
[*]legal protection insurance
[*]other insurances (e.g. travel insurance, funeral insurance)

Living expenses:

[*]groceries €200
[*]restaurant costs
[*]personal care/drugstore
[*]pets (food, vet, medication, stable costs)
[*]medication
[*]clothing
[*]furniture
[*]daycare/school fees (and meal money)
[*]tutoring
[*]school supplies and books
[*]club fees/gym
[*]babysitter
[*]toys
[*]cleaning
[*]TV/video/audio/CDs/DVDs
[*]tickets (football, cinema, concerts etc...)
[*]donations
[*]other

Savings contributions:

[*]vacation
[*]house
[*]retirement provision
[*]hobbies/gifts
[*]other

Other expenses:

[*]maintenance payments?
[*]loans?
[*]other?
[*]Was something forgotten? If so, please specify here!

Total income and expenses:

[*]total income €4500
[*]total expenses
[*]balance
[*]of which sum cold rent and dispensable savings contributions (e.g. savings rate for house)

General information about the property:

[*]How large is the plot?
[*]What are its dimensions?
[*]What is the standard land value?
[*]New building, old building (year built), house type?
[*]Garages?
[*]How large is the house? (living area / usable area)
[*]What is the market value of the plot and house after completion?

Construction or purchase costs:

[*]land costs €25/m2 x 1000 = €27,250 including development
[*]development costs
[*]ancillary acquisition costs (notary, court, property transfer tax, broker)
[*]construction or purchase costs (including architect, structural engineer) approx. €420,000 including garage and outdoor facilities & ancillary costs
[*]renovation and/or refurbishment costs
[*]additional construction costs (e.g. house connections, soil expert, construction power, etc.)
[*]outdoor facilities/terrace, paths, garden design, fences, etc...
[*]financing costs (e.g. fees or commitment interest)
[*]total costs

other costs:

[*]kitchen costs
[*]furniture, lamps, decoration
[*]other "non-acquisition, acquisition ancillary, construction or additional construction costs"

Cost summary:

[*]total costs
[*]deductible equity
[*]financing sum

I have only entered rough information; I hope you can roughly understand what it is about.
Young people, dream of their own property & immense construction costs nowadays. Land is very cheap for this.
Salaries will only rise minimally in the future.
We would also like to reduce costs by personal contribution, e.g. craftsmen in the family for groundwork, masonry. The house maybe only 140m2 instead of 160-170m2 (the €420k is calculated for 170m2).
Whether it complies with KFW standards or not essentially depends on the ratio of additional costs / benefit of the KFW loan. Currently, in my opinion, it does not pay off. Of course, people build with photovoltaics & heat pumps.

Would you finance something like this given the opportunity of cheap plots?

What kind of service technician are you? If I were you, I would look to make use of the things you have. So, use the skills you bring with you. All these subsidies are usually only worth it if you were planning to outsource these trades completely anyway. I completely refrained from them in my construction because then you have free rein.

Just out of curiosity, where are such land prices? Are these developed building plots?

Mechanical engineering, so no experience in house construction. However, experience in the family. I would roughly say: we do the groundwork ourselves up to the slab, masonry work is also done by family/acquaintances... interior finishing, whatever we can do ourselves... preparations for the electrician etc. Doors/windows, plumber, roof structure, painting work I would have done... try to do the exterior facilities ourselves as well. This means the 420k are officially calculated, it should be as cheap as possible. Such land prices only exist in the countryside, I would say a village with 700 inhabitants ;-) It is a (almost fully) developed new building area, where there is still room for improvement regarding internet, for example.... For that, you need a car, shopping facilities etc. are 3 km away. No public transport.

Wow. I also developed a plot of land 3 years ago. It was previously an orchard meadow. Just the development cost more than your plot. It is in the countryside, but our standard land values are a factor of 11 of your m2 price, but that's how it is when you can see the Alps from the terrace...

120sqm house will be fine. With good personal contributions 140sqm (+x). But then 2,000€ will go as "Warmmiete". For me personally, given the future prospects (e.g. children), that would be too much.

With the land prices, you are adW in a structurally weak region. Therefore probably with extremely cheap property prices. My choice would therefore be a used property.