Too bad
You have a net income of 4300 euros after PKV and you want to finance 430k (what about upgrades, outdoor facilities, floors, kitchen, etc.). Is everything really included?! Basically, it should be doable.
But the whole framework is not just based on the installment. Then come the annual or monthly incidental costs. Depending on how big the house gets, you calculate (I think) 2-3 € per sqm.
So I think that just under 40% of your income would be spent on the installment + incidental costs (if you calculate all costs monthly) for housing. Then there are your own monthly expenses like car, leisure, vacation, hobbies, subscriptions, internet, mobile phone, possibly other insurances, etc. pp.
Since children are planned and of course income temporarily decreases and eventually things like daycare come up, personally it would probably be too tight for me as well. The residual debt at the end of the interest rate term after 15 years would also simply be way too high for me.
Actually, (except for the kitchen) everything is included. However, we want to either take the kitchen from our apartment or pay for it separately (we would then hold back at least 10,000 euros and would not need the kitchen until in 18 months). For the beginning, a kitchen for 8,000 euros is also enough for me.
My current calculation looks like this:
4,800 income (or 4,200 in the first year with a child, 4,600 in the second year with a child) - Christmas bonus and tax refund not included
1,200 for the installment
400 incidental costs (with 125 sqm living space, is that realistic?)
500 health insurance
60 disability insurance
100 savings rate
60 Riester (with term life insurance)
180 car (but will drop off in two years)
75 annually incurred costs, divided by 12 months (ADAC, liability, car insurance, car tax...)
40 internet
40 mobiles
50 SKY
That leaves a monthly remainder of 2,095 euros (or 1,495 in the first year with a child and 1,895 in the second year with a child). From that, living expenses (currently around 600 euros including vacations), fuel (about 250 euros) and everything else must be paid; mathematically there should be a surplus of at least 650 euros (which, of course, the baby would also have to live from).
Too risky?