For example getting settled prior to the school year starting for their children in a new school district.

We plan to consult a tax professional but I wanted some general thoughts and considerations prior to that meeting.

I make it clear that my policy is moderate (full refund prior to 5 days of arrival date), also that Airbnb has a no refund price, so that would mean no refunds under any circumstance if they book that.

You got bad advice from your prior accountant.You received rental income and it should have been reported.it seems like maybe he was lazy and/or doesn't understand rental concepts.The only exception is if he is paying 'under-market' for rent in which case the property would be considered personal use.I would fix the issue and charge him market rent. 

I would recommend negotiating prior to going into contract.

Although they had just loaned me 80k 10 months prior and im in the middle of refinancing house 3 to pay back that 80k, they agree to loan me another 200K to purchase the property to both purchase the house  and have some extra money to help with some of my own money to make make renovations.

Last year code enforcement showed up and was "just checking on things" since they had prior history with this house & the people on the property.

Investment in this area tends to be block-by-block so as @Paul De Luca mentioned, it's worth driving through and assessing prior to making any investment decisions.

Certain trades I wouldn't skimp on, like electrician, plumbers, etc, but sometimes you can get away with bringing them in to do the finish only, or you can pay a licensed trade or GC to come and inspect the work prior to closing up walls, etc.

I have golf cart insurance and I have a golf cart waiver that each guest has to agree to prior to making the reservation.