In addition to your income and credit score, lenders will look at your ability to service debt. 

So make sure you have info about the HOA before closing, otherwise delinquent units could impact your ability to sell the unit.2.

At the end of each guest’s stay I mention my website and their ability to save money on fees by booking there so I think it is worthwhile.

These loans don't take into account your personal DTI and mainly care about the properties ability to cash flow.

That will affect your current ability to attract quality renters or receive strong reviews following their stay if made into a STR. 

He will also have the ability to buy additional equity from me on an annual basis, up to the amount he earned in property management fees, for the first n years (n TBD).

My question is what ability we have to enforce certain “policies” such as requirement to maintain renter’s insurance(their leases don’t require it) prescribed method of payment (they currently deliver cash to the landlord’s local bank) or increasing their deposit (some are as low as $100, and one tenant has no deposit at all)?

I find a lot of investors getting bent out of shape in the forums when they get criticism as if another point of view on their "too good to be true" deal is an affront to their ability to scale.

Property mangers are like lawyers, if they even think about your property they send a bill LOL.  

Did you send a letter stating the issue with a bill?