The good news is that the financial metrics you've read about are universal and not at all country specific.The bad news is that Germany may just not be a good cash-flow market, compared to the U.S.But then, few markets are.That's why you find so many Germans and Australians and Spaniards and others trying so hard to find great deals in the U.S.And, even in the States, there are plenty of sub-markets where properties routinely fail the so-called "1% rule."

Meaning how long should I expect to wait for routine repairs to be made?

What you can do right now is connect with an investor-focused real estate agent who has house hacked before or is house hacking now and routinely works with other house hack buyers.

Ask how they handle routine maintenance and emergencies and whether they have established relationships with cost-effective and reliable vendors.By focusing on these critical factors, you’ll be in a solid position to hire a property manager who can take the stress out of managing your rental property while helping you maximize your investment.If anyone has more specific questions, feel free to ask—I am happy to share more detailed advice!

10% is probably a little steep, and like John said, a flat fee may be more reasonable.Setting up a proper STR is not cheap, but once you are set up properly, you deal with routine breakage.I recommend managing yourself and saving the 20% personally, getting a rockstar cleaning team and a reliable handy person, using something like Hospitable that can help automate messaging when listing, and reading the book from the bookstore here called Short-Term Rental, Long-Term Wealth.

I have friends that routinely use ear plugs in a detached single family to eliminate noise from kids, spouses, cars going by on street, etc., when sleeping.

The key is establishing routines and systems that minimize your day-to-day involvement.By using professionals, keeping investments simple, and managing your time efficiently, you can build your real estate portfolio while working full-time. 

If you're going the umbrella insurance route, perhaps see if it will cover you for several things including just the routine slip and fall (like mold or earthquake).

The only way to effectively determine this is by driving neighborhoods, walking properties &  observing the daily routines of those who live there. 

I got my license within the year and I'm having difficulties adopting my brokerages daily routines and general systems.