On top of that, the prices of single family and multi-family homes could be very expensive as well. 

Maybe one day I can sell this system, but right now is for my use and under testing.

With HMLs and cash in place, it sounds like you’re set up for success as you move into BRRRRs and multi-family investments.

Who is going to change the air filters in the HVAC system or mow the lawn?

This includes operating your heating and air-conditioning system as appropriate to reduce humidity, using appropriate ventilation, limiting evaporation of water, promptly removing any visible mold, and immediately reporting to us any leaks or other water intrusion into your apartment or any visible mold that you cannot remove.

Once I have a strong system set up, I don't want to dedicate too much time to real estate, though.It's also important to note that I'm a US citizen who wants to invest in US real estate, but I live abroad.

My first fear for you is that you don't really know much based on your questions and you might need longer to learn it than just trying to get and fund this deal. 22 units, with only 2 multis as experience, makes it harder to find stranger money, but more probably to find friend or family money if that makes sense.

You want that other 15k on the side for reserves, especially if you are buying a multi.

We operate in a broken system that is ripe for abuse and fails to protect us.

I would look into whether you really need a multi-member LLC at this point.