Your "cold rent" increases from 450 to 1,250 EUR. That is the rate. Your additional costs increase from 100 EUR (extremely cheap, does that include ?) to easily 300 EUR.
I would not expect 300 euros additional costs for a single-family house of this size. That is calculated very low for future developments, in my opinion far too low.
Costs are rising everywhere and quickly. Everyone just wants your money. I would plan for 600-700 euros, or even more.
So loan installment + additional costs are already 2,000 euros gone, and tend to increase further. Food costs will certainly increase as well.
Meal money for the child was just increased here as of 01/01/24, which is now over 100 euros per month. (5.30 euros daily)
Your equity practically invites you to build your house much cheaper and to do without a general contractor.
But well, that is up to you.