I agree with Kyle, I would request to see some payment history which would reflect the frequency/stability of the payments

Verify the frequency of the tow company's drive-bys.

There are some clever sleeping quarters shown on AirBnB, The more clever the room, the more it's in demand.So realistically, you could create a themed sleeping nook out of cardboard and improve your booking frequency.

The idea is going to be to use his money as a portion (or all) of the down payment. . .so I'm really trying to ascertain what to do in the way of interest rate, frequency of payout, etc.

You are correct sir, it is much easier to transact in a Solo 401k than it is an SD IRA, especially when time sensitivity or high frequency of payments out are a concern.

I was wondering about the frequency of pest control service in central Florida.

Over that we strap the wall/ceiling with resilient channel - the resilient channel both provides better hold for the sheet rock in the event of a fire {i.e. ceiling stays up longer} and, by suspending the drywall off the floor joist reduces the low frequency sounds/vibrations from the floor above {i.e. running little kids or pets}.  

As I read through the comments, I paid attention to:1) the frequency that a mistake was brought up and 2) the answers with a high number of upvotes.

., deconstruction for tax advantages is a first for me too... in these parts (around the greater DC area) older, smaller houses are being torn down with frequency to build newer, larger ones, and I've yet to dismantle one (nor have I seen any others do it).  

REI Marketing is a 5 - 8 FREQUENCY business.