The rate and income are less of a problem here than the idea of wanting to build at home with an infant. If you’re not a professional and something goes wrong during the construction... good luck, divorce rates are quite high here.
That is, however, a different problem
There are bonus payments and a 13th salary each.
They calculated the following while she stays at home:
Net household income: 3700,-
Loan: 1250,-
Additional costs: 400,-
Living expenses: 1600,-
leaving a buffer of 450,- per month.