I have an online-based retail biz in a niche area of the music industry....also have a business building custom guitars.

For me the series was instrumental in understanding how to make your money work for you instead of working for your money.

When the music stops, I don't want to be looking for a chair.  

That is music to my ears as an investor, so i introduced myself and asked for more details. 

I had to evict people because they didn't quite grasp the fact that living in a duplex means you can't come home from the bar at 3 am and blast music.

Racquetball courts, self-serve/help auto shops, concert halls, music rooms, recording studios all rent space by the time frams used.Closer on topic.Those are the four ways tha real estate provides an economic profit, basically covered in the Principles of Real Estate.

While it might be cool to be a one-man-band (I actually play multiple instruments), it will take one longer to complete jobs if one tries to do everything one's self.

In other words, rather than coming up with 50k cash, could you put a lien on one of the houses or use some other legal document/instrument/contract/etc that in effect gives the lender the right to foreclose on your other property and keep the first 50k of the sale if you default on the 4th mortgage?

Young kids riding around blasting loud music.

So they can't turn their music up, they can't stay up late and all kinds of stuff without fear of having you hear them and not like what they're up to.