Questions with ADA/FHA accessibility provisions

[Joshua H.]

I've recently acquired an old row building that has a commercial space on the first floor and a residential unit above it. Both are currently vacant and are in the process of being renovated. 

Being that the building is over 100 years old, i.e. prior to the 1992 ADA, what ADA/FHA access provisions am I required to supply? The entrance sits roughly 30 inches above the curb and is accessed by three cement steps. The rear of the building is only accessed through a narrow alley. I've read/heard differing opinions on if I am required to modify the entrance to a ramp.

Also being that the commercial space is on the smaller side, 550 sq feet, with only street parking, this lends itself to a business without much traffic. I also don't know whether I, as the property owner, or the future business owner would have to provide the accommodations?