I see it completely differently than nordanney.
This will be a tight or unpleasant situation if you need so much money from the bank!
The times of 1 and 2% interest are over, with 400k, 3% (which by the way, at the moment, you can’t even get if you really have good equity >60%, not like here, where you don’t even have 20%) means 1k in interest per month, what do you pay down then? 400€? and the loan is paid off in just 50 years.
No, you have to rather expect at least 2k and in the end, you still pay a lot of money to the bank that is licking its fingers (no one really believes that).
For a single-family house, the equity is quite low, the income OK - since family planning is still pending, you have to expect a temporary loss of one income.
I find the last point about saving 30k per year most interesting (although the question arises why that has not worked in the past), my approach would be to wait another 3 years, use the time for planning, and then only need 300k from the bank.