Thus the occupancy of the neighborhood plummets, the values plummet because landlords have a hard time selling their units to an owner occupant, and the tenants who want to live there are locked out. 

I am in a very similar situation to what you were in 1 year ago and very interested to see if you pulled the trigger, bought a property and how it went?!

The landlord should hold keys for these doors as well, in case of a lock-out.

Germaine Act that allows anyone to place real estate in their own trust without triggering the due-on-sale clause.

Also, if if I go ahead and buy my first property I would lock in a better rate because it would be O/O. 

The best way to lock a contract with a sponsor is by locating a good deal first and then presenting it to a syndicator to see if they are interested in joining. 

People have done FHA on SFRs with 'one entrance,' and rent the rooms to tenants/roommates.Now if the one entrance grants access to the whole duplex, you might want to find a way to separate the units(Ex: add additional doors with locks for the upstairs and downstairs), unless you're looking for a roommate type of tenant.

I'm going to pull the trigger.

For some reason I thought I read something about LO's triggering DOS.

I am also getting a quote on inspection just in case I want to pull the trigger.