I would like to start with a duplex and build from there but want to know some of your thoughts?

I’m in the midst of cashing out a paid off duplex and easily qualify for for a conventional loan.  

I bought my first deal last year ( a duplex ) which since has been a great investment.

The oil burst up onto the walls and ceiling leaving a residue covering a large area.

Investigating the potential of an additional onto a house for the purposes of going from 2 br 1 ba each duplex, to 3 br, 2 bath each duplex. 

I've seen these things eat chunks of grease-soaked drywall and wood from cabinets, so if  you've got some saturated wood in the cabinet, cleaning the surface won't get rid of them.You might also have to change carpets also - since there's really no way to fully clean carpet...I've also seen german roaches infesting a burned out unit feasting on burned greasy cabinets and walls.   

Simple dry wall and flooring is easy for me.

They also bumped out walls on the 1st floor and added a 2 car garage. 

I sold a duplex in Minneapolis that had at least that much elevation change from front to back.Some people will care, some won't.

I am closing on my first investment here shortly that will be a duplex.