The problem with outbound marketing is exactly what you mentioned above; paying for addresses and numbers that don't respond.Most of the investors that I work with directly have inbound marketing setup as their primary source, and are doing outbound marketing as a small supplemental source of leads.

For the application, does anyone know what you can and cannot ask for, to supplement the income? 

Properties make a fantastic investment opportunity for anyone looking to replace or supplement their income.You enjoy many rewards and boost your profitability to a whole new level.

A good PM should be doing this for you - if that's not happening - you'd be better off spending your effort/time finding a better PM then working on supplemental advertising to theirs 

It's very common to get an interest only loan in the multifamily space.While in the SF space, you do cash-out refi with a new mortgage, it is more common in apartments to get what is called a supplemental loan.   

To supplement other retirement income?

My wife and I are planning on having kids soon and the idea of cash flowing monthly to supplement her income while she stays home more with the kids and to reinvest that cash flow appeals to us.

It is possible to start and flourish without Airbnb simply by talking to the business owners in your town who bring in essential workers to supplement their activities. 

It has definitely helped out A LOT with supplemental income and saving money on my own deals. 

I am venturing into STNL as an income strategy to supplement my income from day job and SFR income.