Refinancing - Tax Consideration?

Nevertheless, interest expenses of a rented property can be counted as costs against the income from the rented property.

Does that also apply if the OP takes out a new loan to raise capital for another property? I somehow thought there was a purpose binding or something like that for it to work. But I don't really know much about it.

The interest costs for the financing of a rented property can be deducted. And yes, these are [Werbungskosten]. For whatever reason.

However, it must be clearly provable that the financing was used for the property. Otherwise, the tax office will calculate something for itself. You might possibly be able to swap the financings through the bank if you have both financings with the same bank, so that you have the higher-interest loan on the [ETW]. Whether this is legally proper, your tax advisor will actually tell you.

The interest costs for the financing of a rented property can be deducted.
And yes, these are advertising costs. For whatever reason.

And indeed advertising costs for the income type "rental," although I prefer to use the term costs there.
And of course, only the interest for the loan that is for the apartment being rented can be deducted as costs from the rental income.

No. It is not the performance of a profession or an employment. You have to be employed somewhere.

I recommend reading § 21 Income Tax Act

If you rent out the [ETW], the interest from the loan from 2017 can be deducted as income-related expenses from the time of rental. The interest from the new loan cannot be claimed, as the apartment in this case only serves to improve the loan-to-value ratio for your privately used house. The new loan therefore does not serve to generate taxable income. These are therefore costs of private living expenses.

The tax office distinguishes only between income-related expenses and operating expenses among the types of income. For the forms [Anlagen N, V, Kap, R, and SO], these are income-related expenses. For the forms [Anlage S and G] or [EÜR], these are operating expenses.

Talk to a good tax advisor. The tax office does not know how high the debts or interest are, as nothing has ever been deducted before.