I suppose that I should have done a bit more research into the nature of promissory notes as financial instruments to answer a couple of my own questions.

If I set up a wireless router and give all of them access to it, can I be held accountable if any of the tenants download illegal music or hack a government website or something?

Just asset backed financial instruments loaned to real estate professionals (hopefully)You can build working capital by flipping homes with your HELOC.

They are loud and always fighting late at night, always banging on the walls, playing music and video games so loud that it vibrates the walls.

The section about LLC's states:The mortgage loan was purchased or securitized by Fannie Mae on or after June 1, 2016, andThe LLC is controlled by the original borrower or the original borrower owns a majority interest in the LLC, and if the transfer results in a permitted change of occupancy type to an investment property, such change does not violate the security instrument (for example, the 12 month occupancy requirement for a principal residence).

From investopedia: Leverage is an investment strategy of using borrowed money—specifically, the use of various financial instruments or borrowed capital—to increase the potential return of an investment.

But that is the instrument you use.. 

I met another investor there that's putting in a micro-brewery/restaurant with a music venue behind the restaurant.

Unsecured loans or lines are much like a Heloc (Home Equity Line Of Credit).Both offer the same competitive rates, both offer a check writing feature, you only pay on what is drawn upon at simple interest and terms generally run at 5 and 7 years.The main difference of course is that a Heloc is backed by your home as collateral and an Unsecured line is only backed by a business guarantee to repay with no collateral such as a mortgage, security instrument or other equity.What are the benefits of an Unsecured Loan?

They bought new cars, new trucks, all sorts of tools and equipment, hired people, etc and when the music stopped playing, they had a giant monthly nut and were sitting on a handful of houses at various stages.