Hi,
this is actually about signing the purchase contract immediately, and registering the mortgage later, once the financing is secured?
so, you are planning total costs of about 550-600 TEUR (All IN)
equity around 200 TEUR
financing around 400 TEUR.
so
1) You can do this independently, meaning sign the purchase contract first and register the mortgages for the bank later.
2) since you are building with a developer, they probably have a payment schedule according to the developer regulation, i.e. probably the first payment will be due immediately after signing (about 4-6 weeks later), since it also includes the land, this is likely unavoidable.
BUT if you can pay it from equity, that would still be ok (but you must also keep money on hand for property transfer tax, notary, etc.!)
so this question would be settled.
back to the financing of 400,000 EUR, with 3200 or after marriage 3700 EUR?
that is of course doable, but quite tight! Depending on the bank they calculate living expenses allowances of 850-1500 EUR here.
Then there are operating costs (taxes, heating costs, electricity, garbage collection, etc.)
then you should consider reserves (in case renovations are necessary)
saving for the next car etc.
then there is not much left for the installment, with a loan amount of 400,000 EUR.
BUT here the assumption is that the better half will also earn money in the near future, so it would increase to at least 5000 EUR, which would be manageable again.