Loan amount - What is achievable?

Phew, so to assess this correctly, you would need to take pen and paper yourself and a) create a balance sheet and b) create an income and expenditure statement.

a) So that it is clear how high the equity really is.
So put the values of the real estate + stocks + cash on the left side
On the right side the liabilities.
I don’t quite understand it yet.
Remaining debt 2028 is useless, what counts is the status today.

b) To determine the disposable income.

Regarding Immo1: Whether it’s worthwhile you can only see based on the exact numbers.
1% interest and 2% repayment means a 40-year term.
Then you would be ~65 to 68.
But as I said, you can judge that better.

For me, the alarm bells go off at the following statement:
"Immo2 is burdened with a mortgage on the parents’ house"
To me, this indicates that there were already problems when taking out this loan.

Now another loan?
I am skeptical about that.

Do you have a financial/asset advisor? The model looks a lot like that. He squeezes everything out of you to get the maximum for himself. Parents’ house encumbered? Someone really wants to know.

The remaining debt at the end of the fixed interest period is less important; rather, the current actual situation counts: I see here (roughly) currently €300,000 total debt. If now another €350,000 - €400,000 were added, you would have €700,000 debt, which (with all due respect) cannot be managed with your current income until retirement. The bank will also tell you that.

Even the first apartment is a catastrophe: 5th-grade math €120,000 debt, €20,000 repayment in 10 years = 60 years until everything is paid off. Add the interest, which could also rise at some point... you'll be 100 years old or older before you have paid it off, WTF!

So purely in terms of liquidity, I actually see no problem, but your creditworthiness will become a problem for a planned house construction.

The first apartment is already a disaster: 5th grade math 120000€ debt, 20000€ repayment in 10 years = 60 years until everything is paid back. Plus the interest, which could also rise at some point... you'll be 100 years old or older before you've paid it off, WTF!

However, it is common with rental properties to repay as little as possible and instead, if possible, achieve positive cash flow. Whether you then use that for special repayments is another question.

In the end, I don't know anyone who, while they themselves started as small landlords, also took on home ownership. You can certainly do both in parallel once you reach a certain size, meaning with a certain income. My advice here would be to focus on one. The necessary scale simply isn't there.

So the thing with the parental home simply comes from the fact that I bought my apartment during my student days. Because of that, I had the same installment as if I had paid rent, but with the difference that I was paying off my apartment (although not much) and on top of that, there is the not insignificant increase in value since 2012... So I think that was a great deal for me!
The mortgage on the parental home is low and therefore back then as well as now does not pose a threat. The apartment cost 85,000 in its unrenovated condition (I did most of it myself + converted the attic) (no realtor). The increase in value simply comes from the renovation, the attic conversion which doubled the living space, and the positive value development over the last 6 years.
Reserves for the house are there. The heating was completely renewed 6 years ago (including pipes) and reserves for a roof renovation that is due in the coming years are available. So not that much can come up. Also, vacancy in the Munich catchment area is currently absolutely no problem. That’s why I still think it was good to buy this apartment during my student days.
The second apartment, which is currently rented out, is in the same building. I got this at a fair price and without a realtor. I bought it and split the mortgage on the two apartments. It was basically planned to be a self-runner as shown in post #14.
Then there’s just a loan running until I’m 65... As long as it’s covered by the rent, I just have to buy laminate every few years and renovate the bathroom now and then, that’s good, right?
Besides that, after the first fixed interest period (the installment doesn’t change until then anyway), I can still sell if the interest rates are so high by then that the rent doesn’t cover refinancing.
I got my currently inhabited apartment so cheaply that in my opinion there isn’t much risk involved.
Those were my motives and thoughts for acting the way I did.
But I will take it to heart, sit down again and think about whether a sale might be more sensible, which is the overall tenor here.

The remaining debt at the end of the fixed interest period is less important; rather, the current actual situation counts: I see here (roughly estimated) currently €300,000 total debt.

that is already calculated very generously...
According to my 5th-grade math knowledge, 120k + 65k + 40k is actually 225k

The very first apartment is a disaster: math grade 5, 120,000€ debt, 20,000€ repayment in 10 years = 60 years until everything would be paid back. Plus the interest, which could also rise at some point... you'd be 100 years old or older before you've paid it off, WTF!

Sure, I haven't paid off much after 10 years, that's true. But at least 25,000 are gone and in that time I got 30,000 euros (gross) more rent than I paid in bank installments.

That means if the property prices stay constant for 10 years, I'll be able to sell the apartment again for 110,000, can pay off my loan, and still have 15,000 left as additional income for 10 years.

Net, the apartment yields around 400 euros per month (without going into the exact tax aspects, depreciation, etc.). That means I earn 100 euros x 12 months x 10 years = 12,000 euros from the apartment minus possibly some minor repairs.

That means as long as I don't have to sell the apartment for less than 95,000 remaining debt - 12,000 net rent = 83,000 euros (which would correspond to a loss in value of about 25%), I'm still breaking even. That would be the worst case.
Maybe prices will rise in 10 years or stay constant? Nobody knows... Personally, I consider a drop of 25% rather unlikely.