Real estate as an addition - security to get a good interest rate

Perhaps as another approach: If a KfW loan is an option, it is considered a substitute for equity by some institutions. So, for example, if you build according to KfW55 or better and take out a KfW loan of over 100,000 EUR, this does not reduce the loan-to-value ratio and can thus lead to better conditions.

KFW funding usually does not reduce the loan-to-value ratio if it is registered in first priority! The loan is only granted by the lending bank and therefore does not lead to better conditions. Unless your equity ratio is so good that another bank takes a subordinated position with the KfW loan, then you will also get better conditions.