Your worst enemy here is moisture, so yes make sure your HVAC system is working properly and make it clear to the tenant that they notify you of any dramatic changes to the floor or noticeable water damage.

Then it costs $200-250 to do worst case. 

We always hear of the home horrors and brace ourselves for the worst.

I'm leaning the same.I want these aholes out of my house before they damage it more or cause more issues. 2nd worst tenant ever. 

Worst case you buy the house, it breaks-even-ish for a while and then California becomes an investing wasteland and your equity in that property and your duplex go to zero. 

It will always break at the worst possible time.

First, a house that old will NEVER have a flat floor, so you need to live/minimize the worst. 

Worst case scenario we pay more for housing than we are currently but would be able to get by, best case we would have a very good investment property.

Sometimes the people you think you want out the worst end up having another tenant trump them with worst habits or worst payment history.

Worst house on the block in a good area.