If only one lot is empty, I would check if it is in a flood zone, or if there is storm water easement in the back or side.

The rent from my roommate and the second unit of the duplex cover my mortgage, insurance, taxes, maintenance, cap ex, vacancies, heat, electric, water, and internet!

@Jesse Waters I have asked about Blakent loans but didn't get much of a response from the lenders I asked.

That's a solid indicator that they overpriced it...which will at least give you an idea of what it isn't worth.Sounds like a very unique/historic property, which may limit your pool of potential buyers.

I know there's enough space to convert, but I'm interested in understanding the path better.I know I have to (not in order of importance):1) add an additional entrance for 2nd unit2) convert a bedroom into a kitchen plus3) get additional electric/gas service4) submeter water?

If you are buying and holding then the nets to work into your analyses would be: (1) mortgage, (2) maintenance fees, (3) property taxes, (4) homeowners insurance, (5) water bill, (6) property manager if you do not intend to manage it yourself, and (7) future property maintenance, suchas roof & painting, and concrete.  

@Mike Hurney,thought about and tried that more than once....under water between 10-15k everytime I had my realtor buddy call in favors to bank appraisors 

The asking price is just a little bit more than the land is worth plus improvements such as, water hookup and sewer hookup and electrical not counting house.any rate, we can come up with the difference plus down payment of course. the house the seller and I agree, its not forgettable.

The drain backed up and downstairs toilet overflowed with what smelled like sewage water.

Needs new roof, kitchen, water heater etc?