Since it's ideal to approve a rental applicant with income 3 times the rent, I wonder if combined income of multiple applicants over 18 who will be living in the unit qualifies this requirement? 

As far as tenants you get the leases, ledgers can ask for application packages (rarely provided) and the estoppel's but from there you do nothing on the tenant side until you are the owner. 

If the tenant does not qualify on their own and you don't want the entanglement of a co-signor then move to the next applicant. 

Listings, screenings, showings, applications, leases, managing tenant issues... 

There is potential it could change in the future with the city plan, I could try to get a legal non-conforming letter from the city if its applicable and/or try to rezone it but what if I'm not approved?

I would go a step further and actually call the current offerings and get details - security deposits, who pays utilities, application fees, what's their process for viewing and applying, etc. 

We also are able to fill many of our vacancies before we put the house on the market because of the backlog of applicants.

The listing brokers job is to sell whatever it is the sellers give them whether great, mediocre, or a bad property.Alot of NNN buildings are simply block boxes with gingerbread (exterior application) on the outside.

Purchasing a home FHA can put you on the road to having good credit because they basically require applicants to settle most debt prior to submission.hope this helps....

Key criteria, in my opinion, should be -1) Stable government & non-corrupt officials - carribean tax havens with glittering opportunities and such, often turn to an investors graveyard, as the government, police or local influentials can make your property (and visa, and permission to enter or trade in the country) disappear in a single phone call.