1890 home, maintenance questions and 2 unit question. Indiana

[Robert Posta]

Hello all, I may have found my first unit to purchase.   It is located in the Midwest.
My question goes out to others that have purchased older homes along with experienced 2 unit landlords.

First off, the home is older and cosmetically in great condition inside and out . It was built in 1890.

The home has a cinder block basement and siding for the exterior.
What things should I look for that may be hidden.  I know pipes are a big issue. 
The home is on city sewer/water. It might be worth a plumber to send a camera down the main sewer to check the condition. 
I would love any tips from others on what to look for.

The home has separate meter for gas and electric. It has 2 units.
The current owner did not use it as a rental and uses the whole home (both units ).

What is the best way to go about making sure these are legal 2 units?
The numbers look great so far and my only worry is this may be a money pit due to the age. 
I am going off of pictures now and I am working on a showing next week. 

I am really interested and it may go fast. If I like what I see I am guessing I should put an offer In with contingencies?

Thanks so much for any help and assistance.