House purchase from uncle - Monthly payment or take a loan?

The purchase price is €300,000 My current assets amount to around €200,000

Option 2: I take out a loan of €200,000 or even €300,000 and pay him the purchase price of €300,000 directly.

Why should you take out a loan of €200k or even €300k if you already have €200k in equity??

As for the fundamental question: take out €100k, add your equity, pay him in full, and everything is settled. Pharmacy and horses, etc... there was always pure sunshine in the family, everyone got along "great"... no one ever "complained"... then an inheritance became due... --> 2 out of 6 still talk to each other, the rest partly through lawyers. 6 out of 6 would have said a few years ago that it would never come to this. Make a clean break, my advice.

Edit: Gerd and Dieter were both quicker ;)

So I definitely want to leave around €150,000 invested in stocks, hence the idea of borrowing €200,000 or €300,000 in the case of option 2.

We have already had several inheritance cases in the family, and so far there has never been any dispute.

I will inherit 1/5 of his assets with my 4 cousins (my uncle has no children), so in the event of death I could also pay out all of them with the inheritance.

Is the property revalued in the event of death if there is a purchase contract for €300,000 and, let's just say, €100,000 has already been paid off? I can't imagine that. Then I probably owe each of the other 4 heirs €40,000 and have to pay 20% gift tax on my share of €40,000. I would be surprised if the property is then revalued and costs more than €300,000.

Now the question is, what is financially more reasonable for me?

The question cannot be answered on its own. An important piece of information is missing.
Owner-occupancy or rental.

In the case of rental, the focus is more on tax optimization. So a high loan - no matter where from.
In the case of owner-occupancy, usually a low loan. Unless you believe that you can earn significantly more in the stock market than the additional interest costs in financing.

I am buying the property purely for personal use.

In addition, I want to renovate for around €100,000 in the next 1-3 years + not liquidate all stocks, so I don’t like it when I use all my money for the purchase now.

The cleanest option is the complete purchase and full payment. This also keeps everything clear in your mind. I think the suggestion to borrow part of the purchase price from your uncle is good. In this case, you have a low interest rate and everything stays within the family. Otherwise, use a bank. In the case of installment payments, the transfer of ownership must be monitored. If the property is entirely in your ownership upon your uncle’s death, any potential increase in value will naturally and rightfully also benefit the other heirs, as they inherit ownership proportionally and the value of the property is determined. The idea of keeping a portfolio is understandable and, in my opinion, also sensible given the low interest rates and the risk considerations, as long as the income securely covers the obligations.

Do the heirs not only inherit the amounts from the purchase contract? This practically nullifies the purchase contract. Perhaps this can still be stipulated in the purchase contract by the notary