Duplexes on the other hand might be a bit more stable as they are all 'investment' properties whether the owner lives on one side or not.

How stable are they? 

You would need to invest in  stables.

but suffice it to say.. buy quality assets in a very stable market..

Stable type of investment. built to sell.Plan is to develop others.

Which neighborhoods and types of housing will appreciate and why – not just what the next hot neighborhood is, but where fellow investors believe long-term stable growth will occur.

is the contractor financially stable?

For secure long-term growth, look for stable neighborhoods that are good for long-term appreciation at consistent levels.

My father is very close to retirement as well and one of the reasons why I am considering making this move is that one, I will have a family member with stable income renting the property, my father will be able to help manage the property and take care of it while I am away, and the extra income would definitely be very useful in NYC.

as it is, I'm not sure you can get deeper in debt without stable employment and a plan for the future.