Thanks for a few tips
Your numbers:
+ House & land 230,000 euros
+ Conversion/renovation 100,000 euros
Subtotal 330,000 euros
+ Additional costs 28,000 euros
Total 358,000 euros
- Equity 23,000 euros
Loan requirement 335,000 euros (102% of the subtotal).
With the bare numbers you are already over 100% lending. For conversions/renovations, usually not all costs are recognized as value-increasing, so your loan-to-value ratio is likely even higher.
With this high loan-to-value, an initial repayment of 3% is probably appropriate, maybe even required. Let’s assume you get the money at an interest rate of also 3% p.a. That results in an annuity of (3+3=6)%. So 335,000*6% / 12 = 1,675 euros/month. That is noticeably above the desired installment.
At the desired installment, an interest rate of 1.66% p.a. would have to be offered (with 3% initial repayment). If you repay only 2%, the interest rate can already be 2.66%. Depending on your creditworthiness, however, this is already difficult at this loan-to-value.
A lower initial repayment only shifts the problem into the future and would make it difficult to find a bank. The interest rate improves with more equity and/or a shorter term.
On the topic of Wohnriester: I would always ask the bank to offer me a completely normal annuity loan. If several banks reject you, then reconsider the project.