But understanding why it has been vacant for 12 years is the key here.

I have already done everything on list so far except the key words.

Could someone just have filled the basement with sand and boarded it up, or is it possible that the foundation is built on ground level? 

At the airport waiting to board the plane now.

To deal with the changes in height that are in the transitions between rooms, I'm thinking about using various width boards to build custom height floor transition/ thresholds between each room. 

I have been noticing more and more turn-key multi-family homes for sale in my area (Rochester, NY).

Key to knowing how the second will play out, is knowing who the investor is on the first. 

As was mentioned above - Relationship is key when it comes to real estate banking and financing - the ability to get a mortgage with a "phone call" is very helpful.

So no boarding up the window or turn off the electric.  

We are lucky to have a strong HOA board (that my husband and I now serve on, as well) so it's been a great set up for us.